r"""
Morphisms between Surfaces
.. NOTE::
Typically, morphisms are actual maps between surfaces that preserve the
structure of the surface. In this case, such morphisms live in the
appropriate category. However, sometimes, morphisms are not meaningful on
the points of a surface but just on homology say.
We aim to encode this in the category of the morphism to some extent. For
example, a morphism in the category of translation surfaces, is preserving
the structure of a translation surface. A morphism in the category of
objects, on the other hand, is not preserving any structure of a
topological space but just meaningful in some other context.
.. NOTE::
Our morphism infrastructure contains quite a few workarounds to make the
SageMath machinery work. The fundamental problem that we are facing is that
our parents (surfaces) are not unique representations. However, surfaces do
implement equality if they are indistinguishable (and this is a good idea
to make pickling work.) SageMath has the assumption that if S == T (which
in SageMath normally implies S is T) that then Hom(S) is Hom(T). We could
implement this, but then Hom(T).domain() is not T but S. Instead, we opted
for tricking the coercion machinery into allowing our non-unique homsets.
Namely, when comparing morphisms, we do not coerce them into a common
parent first but compare them directly.
EXAMPLES:
We can use morphisms to follow a surface through a retriangulation process::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: morphism = S.subdivide_edges(3)
sage: morphism = morphism.codomain().triangulate() * morphism
sage: T = morphism.codomain()
sage: morphism
Composite morphism:
From: Translation Surface in H_2(2) built from a regular octagon
To: Triangulation of Translation Surface in H_2(2, 0^8) built from a regular octagon with 16 marked vertices
Defn: Edge-Subdivision morphism:
From: Translation Surface in H_2(2) built from a regular octagon
To: Translation Surface in H_2(2, 0^8) built from a regular octagon with 16 marked vertices
then Triangulation morphism:
From: Translation Surface in H_2(2, 0^8) built from a regular octagon with 16 marked vertices
To: Triangulation of Translation Surface in H_2(2, 0^8) built from a regular octagon with 16 marked vertices
We can then map points through the morphism::
sage: p = S(0, (0, 0))
sage: p
Vertex 0 of polygon 0
sage: q = morphism(p)
sage: q
Vertex 0 of polygon (0, 10)
A non-singular point::
sage: p = S(0, (1, 1))
sage: p
Point (1, 1) of polygon 0
sage: q = morphism(p)
sage: q
Point (1, 1) of polygon (0, 7)
"""
# ********************************************************************
# This file is part of sage-flatsurf.
#
# Copyright (C) 2023-2024 Julian Rüth
#
# sage-flatsurf is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# sage-flatsurf is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with sage-flatsurf. If not, see <https://www.gnu.org/licenses/>.
# ********************************************************************
from sage.categories.homset import Homset
from sage.misc.cachefunc import cached_method
from sage.categories.morphism import Morphism, IdentityMorphism as IdentityMorphism_sage
from sage.structure.unique_representation import UniqueRepresentation
from sage.rings.ring import Ring
from flatsurf.geometry.surface import OrientedSimilaritySurface
[docs]
class UnknownRing(UniqueRepresentation, Ring):
r"""
A placeholder for a SageMath ring that has been lost in the process of
creating a morphism.
Ideally, every morphism has a domain and a codomain. However, when
migrating code that did not produce a morphism originally, it can be
complicated to get a hold of the actual domain/codomain of a morphism.
Instead, it is often convenient to set the domain/codomain to ``None``,
i.e., stating that the domain/codomain is unknown. When this happens, also
the ring over which the domain/codomain is defined is technically unknown.
We use this placeholder ring in these situations since a surface requires a
ring it is defined over.
This ring provides no functionality other than being in the category of
rings.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: triangulation = S.triangulate(in_place=True)
doctest:warning
...
UserWarning: in-place triangulation has been deprecated and the in_place keyword argument will be removed from triangulate() in a future version of sage-flatsurf
sage: triangulation.domain()
Unknown Surface
sage: triangulation.domain().base_ring()
The Unknown Ring
TESTS::
sage: from flatsurf.geometry.morphism import UnknownRing
sage: isinstance(triangulation.domain().base_ring(), UnknownRing)
True
sage: isinstance(triangulation.codomain().base_ring(), UnknownRing)
False
sage: TestSuite(triangulation.codomain().base_ring()).run()
"""
[docs]
def __init__(self):
from sage.all import ZZ
super().__init__(ZZ)
def _repr_(self):
r"""
Return a printable representation of this ring.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: triangulation = S.triangulate(in_place=True)
doctest:warning
...
UserWarning: in-place triangulation has been deprecated and the in_place keyword argument will be removed from triangulate() in a future version of sage-flatsurf
sage: triangulation.domain().base_ring()
The Unknown Ring
"""
return "The Unknown Ring"
[docs]
class UnknownSurface(UniqueRepresentation, OrientedSimilaritySurface):
r"""
A placeholder surface for a morphism's domain or codomain when that
codomain is unknown or mutable.
In SageMath a morphism must have an explicit domain and codomain. However,
the domain of a morphism might not actually be known, for example when
deforming a mutable surface, or exposing it might break things when it is
mutable.
In such cases, we replace the domain with this unknown surface which has no
functionality other than being a surface.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S
Translation Surface built from a square
sage: triangulation = S.triangulate()
sage: triangulation.domain()
Unknown Surface
sage: triangulation.codomain()
Triangulation of Translation Surface in H_1(0) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import UnknownSurface
sage: isinstance(triangulation.domain(), UnknownSurface)
True
sage: TestSuite(triangulation.domain()).run()
For pragmatic reasons, all unknown surfaces are equal. Mathematically, this
is not correct but otherwise pickling breaks and we need a lot of special
casing for the unknown surfaces everywhere::
sage: triangulation.domain() is S.triangulate().domain()
True
"""
[docs]
def is_mutable(self):
r"""
Return whether this surface can be mutated.
Since nothing about this surface can be changed, we return that it is immutable.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S.is_mutable()
False
"""
return False
def _an_element_(self):
r"""
Return a point on this surface for testing.
Since this surface cannot represent any points, we throw an error.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S._an_element_()
Traceback (most recent call last):
...
NotImplementedError: cannot produce points in an unknown surface
"""
raise NotImplementedError("cannot produce points in an unknown surface")
[docs]
def roots(self):
r"""
Return the root labels of the connected components of this surface.
Since this surface doesn't really have any labels, we throw an error.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S.roots()
Traceback (most recent call last):
...
NotImplementedError: cannot determine root labels in an unknown surface
"""
raise NotImplementedError("cannot determine root labels in an unknown surface")
[docs]
def is_finite_type(self):
r"""
Return whether this surface is built from a finite number of polygons.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S.is_finite_type()
True
"""
if self in self.category().FiniteType():
return True
if self in self.category().InfiniteType():
return False
raise NotImplementedError(
"cannot determine whether an unknown surface is of finite type"
)
[docs]
def is_compact(self):
r"""
Return whether this surface is compact as a topological space.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S.is_compact()
True
"""
if self in self.category().Compact():
return True
raise NotImplementedError(
"cannot determine whether an unknown surface is compact"
)
[docs]
def is_with_boundary(self):
r"""
Return whether this surface has a boundary of unglued edges.
Since we do not record whether this unknown surface stands in for a
surface that has a boundary, we throw an error.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S.is_with_boundary()
Traceback (most recent call last):
...
NotImplementedError: cannot determine whether an unknown surface has boundary
"""
if self in self.category().WithBoundary():
return True
if self in self.category().WithoutBoundary():
return False
raise NotImplementedError(
"cannot determine whether an unknown surface has boundary"
)
[docs]
def opposite_edge(self, label, edge):
r"""
Return the edge that is glued to the ``edge`` of the polygon with
``label``.
Since we do not know anything about the gluings of this surface, we
throw an error.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S.opposite_edge(0, 0)
Traceback (most recent call last):
...
NotImplementedError: cannot determine how the unknown surface is glued
"""
raise NotImplementedError("cannot determine how the unknown surface is glued")
[docs]
def polygon(self, label):
r"""
Return the polygon with ``label``.
Since we do not know the polygons that make up this surface, we throw an error.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S.polygon(0)
Traceback (most recent call last):
...
NotImplementedError: cannot determine polygons of the unknown surface
"""
raise NotImplementedError("cannot determine polygons of the unknown surface")
def _test_an_element(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_components(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_elements(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_elements_eq_reflexive(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_elements_eq_symmetric(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_elements_eq_transitive(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_elements_neq(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_gluings(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_labels_polygons(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_refined_category(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_some_elements(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_polygons(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_eq_surface(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _test_labels(self, **options):
# This generic tests does not make sense on the unknown surface and is herefore disabled.
pass
def _repr_(self):
r"""
Return a printable representation of this surface.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.square_torus()
sage: S = MutableOrientedSimilaritySurface.from_surface(S)
sage: S = S.triangulate(in_place=False).domain()
sage: S
Unknown Surface
"""
return "Unknown Surface"
[docs]
class MorphismSpace(Homset):
r"""
A set of morphisms between structures attached to surfaces.
This is a base class for surface morphisms but also for other structures
such as morphisms in homology.
.. NOTE::
Since surfaces are not unique parents, we need to override some
functionality of the SageMath Homset here to make pickling work
correctly.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: triangulation = S.triangulate()
sage: homset = triangulation.parent()
sage: homset
Surface Morphisms from Translation Surface in H_2(2) built from 3 squares to Triangulation of Translation Surface in H_2(2) built from 3 squares
TESTS::
sage: from flatsurf.geometry.morphism import SurfaceMorphismSpace
sage: isinstance(homset, SurfaceMorphismSpace)
True
sage: TestSuite(homset).run()
"""
[docs]
def base_ring(self):
r"""
Return the base ring of this morphism space.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: S.triangulate().base_ring()
Rational Field
"""
base_ring = super().base_ring()
if base_ring is not None:
return base_ring
if (
self._structure_preserving()
and self.domain().base_ring() is self.codomain().base_ring()
):
return self.domain().base_ring()
import warnings
warnings.warn(
"This morphism set has no base ring. Are you trying to get the base ring of a surface? Use .codomain().base_ring() instead."
)
return self.codomain().base_ring()
def _an_element_(self):
r"""
Return a morphism in this set (for testing.)
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S).an_element()
Identity endomorphism of Translation Surface in H_2(2) built from 3 squares
"""
if self.is_endomorphism_set():
return self.identity()
raise NotImplementedError(
f"cannot create a morphism from {self.domain()} to {self.codomain()} yet"
)
[docs]
def identity(self):
r"""
Return the identical morphism from the domain to the codomain of this
space.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S).identity()
Identity endomorphism of Translation Surface in H_2(2) built from 3 squares
"""
raise NotImplementedError(
"this morphism space does not implement an identity morphism yet"
)
@cached_method
def _structure_preserving(self):
r"""
Return whether morphisms in this space are preserving all structure
(that can be preserved.)
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S).identity().parent()._structure_preserving()
True
"""
# We don't use category_of because it adds a layer of caching that is
# incompatible with our non-uniqueness of surfaces.
from sage.all import Hom
return (
self.homset_category()
== Hom(self.domain(), self.codomain()).homset_category()
)
def _test_an_element(self, **options):
r"""
Test whether :meth:`_an_element_` has been implemented correctly.
This test is disabled when :meth:`_an_element_` is not functional.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S)._test_an_element()
"""
try:
self._an_element_()
except NotImplementedError:
return
super()._test_an_element(**options)
def _test_elements(self, **options):
r"""
Test whether the morphims in this space are functional.
This test is disabled if we have no means to create elements in this
space for testing.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S)._test_elements()
"""
try:
self._an_element_()
except NotImplementedError:
return
super()._test_elements(**options)
def _test_elements_eq_reflexive(self, **options):
r"""
Test whether the morphisms implement `==` correctly.
This test is disabled if we have no means to create elements in this
space for testing.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S)._test_elements_eq_reflexive()
"""
try:
self._an_element_()
except NotImplementedError:
return
super()._test_elements_eq_reflexive(**options)
def _test_elements_eq_symmetric(self, **options):
r"""
Test whether the morphisms implement `==` correctly.
This test is disabled if we have no means to create elements in this
space for testing.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S)._test_elements_eq_symmetric()
"""
try:
self._an_element_()
except NotImplementedError:
return
super()._test_elements_eq_symmetric(**options)
def _test_elements_eq_transitive(self, **options):
r"""
Test whether the morphisms implement `==` correctly.
This test is disabled if we have no means to create elements in this
space for testing.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S)._test_elements_eq_transitive()
"""
try:
self._an_element_()
except NotImplementedError:
return
super()._test_elements_eq_transitive(**options)
def _test_elements_neq(self, **options):
r"""
Test whether the morphisms implement `!=` correctly.
This test is disabled if we have no means to create elements in this
space for testing.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S)._test_elements_neq()
"""
try:
self._an_element_()
except NotImplementedError:
return
super()._test_elements_neq(**options)
def _test_some_elements(self, **options):
r"""
Test whether the morphisms implement :meth:`some_elements` correctly.
This test is disabled if we have no means to create elements in this
space for testing.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S)._test_some_elements()
"""
try:
self._an_element_()
except NotImplementedError:
return
super()._test_some_elements(**options)
[docs]
def __reduce__(self):
r"""
Return a serializable version of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: loads(dumps(End(S))) == End(S)
True
"""
raise NotImplementedError("this morphism space does not implement pickling yet")
[docs]
class SurfaceMorphismSpace(MorphismSpace):
r"""
The set of morphisms from surface ``domain`` to surface ``codomain``.
.. NOTE::
Since surfaces are not unique parents, we need to override some
functionality of the SageMath Homset here to make pickling work
correctly.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: identity = End(S).identity()
sage: endset = identity.parent()
sage: endset
Surface Endomorphisms of Translation Surface in H_2(2) built from 3 squares
TESTS::
sage: from flatsurf.geometry.morphism import SurfaceMorphismSpace
sage: isinstance(endset, SurfaceMorphismSpace)
True
There is a bogus warning produced by the test suite for magmas. This will
disappear once we remove the :meth:`__getattr`` hack but is not actually a
deprecation otherwise::
sage: TestSuite(endset).run()
doctest:warning
...
UserWarning: This methods returns a morphism instead of a surface. Use .codomain().is_mutable to access the surface instead of the morphism.
"""
[docs]
def identity(self):
r"""
Return the identical morphism from the domain to the codomain of this
space.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S).identity()
Identity endomorphism of Translation Surface in H_2(2) built from 3 squares
"""
if self.is_endomorphism_set():
return IdentityMorphism._create_morphism(self.domain())
return super().identity()
[docs]
def __repr__(self):
r"""
Return a printable representation of this space.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S)
Surface Endomorphisms of Translation Surface in H_2(2) built from 3 squares
"""
type = "Surface Morphisms"
spaces = f"from {self.domain()!r} to {self.codomain()!r}"
if self.domain() == self.codomain():
type = "Surface Endomorphisms"
spaces = f"of {self.domain()!r}"
if self._structure_preserving():
return f"{type} {spaces}"
return f"{type} in {self.homset_category()} {spaces}"
[docs]
def __reduce__(self):
r"""
Return a serializable version of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: loads(dumps(End(S))) == End(S)
True
"""
return SurfaceMorphismSpace, (
self.domain(),
self.codomain(),
self.homset_category(),
)
[docs]
def __eq__(self, other):
r"""
Return whether this space is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: End(S) == End(S)
True
"""
if not isinstance(other, SurfaceMorphismSpace):
return False
return (
self.domain() == other.domain()
and self.codomain() == other.codomain()
and self.category() == other.category()
)
[docs]
def __hash__(self):
r"""
Return a hash value for this space that is compatible with
:meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: hash(End(S)) == hash(End(S))
True
"""
return hash((self.domain(), self.codomain()))
[docs]
class SurfaceMorphism(Morphism):
r"""
Abstract base class for all morphisms that map from a ``domain`` surface to
a ``codomain`` surface.
INPUT:
- ``domain`` -- a surface or ``None``; if ``None`` (or if the domain is
mutable), the domain is replaced with the :class:`UnknownSurface` which
means that almost all queries related to the domain are going to fail.
- ``codomain`` -- a surface or ``None``; if ``None`` (or if the codomain is
mutable), the codomain is replaced with the :class:`UnknownSurface` which
means that almost all queries related to the codomain are going to fail.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism.domain()
Translation Surface in H_1(0) built from a square
sage: morphism.codomain()
Translation Surface in H_1(0) built from a rectangle
TESTS::
sage: from flatsurf.geometry.morphism import SurfaceMorphism
sage: isinstance(morphism, SurfaceMorphism)
True
"""
@classmethod
def _parent(cls, domain, codomain, category=None):
r"""
Return the homset containing the surface morphisms from ``domain`` to
``codomain``.
This is a helper method for :meth:`_create_morphism`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: from flatsurf.geometry.morphism import SurfaceMorphism
sage: SurfaceMorphism._parent(S, S)
Surface Endomorphisms of Translation Surface in H_1(0) built from a square
"""
if domain is None:
domain = UnknownSurface(UnknownRing())
if codomain is None:
codomain = UnknownSurface(UnknownRing())
if category is None:
category = cls._category(domain, codomain)
if domain.is_mutable():
domain = UnknownSurface(domain.base_ring(), category=domain.category())
if codomain.is_mutable():
codomain = UnknownSurface(
codomain.base_ring(), category=codomain.category()
)
return SurfaceMorphismSpace(domain, codomain, category=category)
@classmethod
def _category(cls, domain, codomain):
r"""
Return the category for a morphism of this type from ``domain`` to
``codomain``.
This is a helper method for :meth:`_create_morphism`.
Morphisms most override this method if they do not preserve structure
(of the join of the domain and codomain.)
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: from flatsurf.geometry.morphism import SurfaceMorphism
sage: SurfaceMorphism._category(S, S)
Category of connected without boundary finite type translation surfaces
"""
return domain.category() & codomain.category()
@classmethod
def _create_morphism(cls, domain, codomain, *args, category=None, **kwargs):
r"""
Return a morphism of this type from ``domain`` to ``codomain``.
Any additional parameters are passed on the to the constructor of this
type.
.. NOTE::
All morphisms must be created through this method so that they have
their parent and category set correctly.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: from flatsurf.geometry.morphism import IdentityMorphism
sage: IdentityMorphism._create_morphism(S)
Identity endomorphism of Translation Surface in H_1(0) built from a square
"""
parent = cls._parent(domain, codomain, category=category)
return parent.__make_element_class__(cls)(parent, *args, **kwargs)
[docs]
def __getattr__(self, name):
r"""
Redirect attribute lookup to the codomain.
EXAMPLES:
A lot of methods that used to return a surface now return a morphism.
To make transition of existing code easier, we look up attributes that
cannot be found on the morphism up on the codomain and issue a
deprecation warning::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism.is_triangulated()
doctest:warning
...
UserWarning: This methods returns a morphism instead of a surface. Use .codomain().is_triangulated to access the surface instead of the morphism.
False
sage: morphism.codomain().is_triangulated()
False
sage: morphism.is_foo()
Traceback (most recent call last):
...
AttributeError: ... has no attribute 'is_foo'
"""
if name in ["__cached_methods", "_cached_methods"]:
# Do not redirect __cached_methods to the surface since we do not
# want to get the morphism and the surface cache mixed up.
raise AttributeError(f"'{type(self)}' has no attribute '{name}'")
try:
attr = getattr(self.codomain(), name)
except AttributeError:
raise AttributeError(f"'{type(self)}' has no attribute '{name}'")
import warnings
warnings.warn(
f"This methods returns a morphism instead of a surface. Use .codomain().{name} to access the surface instead of the morphism."
)
return attr
[docs]
def section(self):
r"""
Return a section of this morphism from its codomain to its domain.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism.section()
Linear morphism:
From: Translation Surface in H_1(0) built from a rectangle
To: Translation Surface in H_1(0) built from a square
Defn: [1/2 0]
[ 0 1]
"""
return SectionMorphism._create_morphism(self)
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
"""
return type(self).__name__
[docs]
def __call__(self, x):
r"""
Return the image of ``x`` under this morphism.
INPUT:
- ``x`` -- a point of the domain of this morphism or an object defined
on the domain such as a homology class, a saddle connection or a
cohomology class. (Mapping of most of these inputs might not be
implemented, either because it makes no real mathematical sense or
because it has simply not been implemented yet.)
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
The image of a point::
sage: morphism(S(0, (1/2, 0)))
Point (1, 0) of polygon 0
sage: morphism(_)
Traceback (most recent call last):
...
ValueError: point must be in the domain of this morphism
TESTS::
sage: morphism(42)
Traceback (most recent call last):
...
NotImplementedError: cannot map Integer through ...
"""
from flatsurf.geometry.surface_objects import SurfacePoint
if isinstance(x, SurfacePoint):
if x.parent() is not self.domain():
raise ValueError("point must be in the domain of this morphism")
image = self._image_point(x)
assert image.parent() is self.codomain()
return image
raise NotImplementedError(f"cannot map {type(x).__name__} through {self} yet")
def _image_point(self, p):
r"""
Return the image of the surface point ``p`` under this morphism.
This is a helper method for :meth:`__call__`.
Subclasses should implement this method if the morphism is meaningful
on the level of points.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
The image of a point::
sage: morphism(S(0, (1/2, 0))) # indirect doctest
Point (1, 0) of polygon 0
"""
raise NotImplementedError(
f"a {type(self).__name__} cannot compute the image of a point yet"
)
def _section_point(self, q):
r"""
Return a preimage of the surface point ``q`` under this morphism.
This is a helper method for :meth:`__call__` of the :meth:`section`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: T = morphism.codomain()
sage: q = T(0, (1, 0)); q
Point (1, 0) of polygon 0
sage: (morphism * morphism.section())(q)
Point (1, 0) of polygon 0
"""
raise NotImplementedError(
f"a {type(self).__name__} cannot compute a preimage of a point yet"
)
def _test_section_point(self, **options):
r"""
Verify that :meth:`_section_point` actually produces a section.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism._test_section_point()
"""
tester = self._tester(**options)
section = self.section()
identity = self * section
for q in tester.some_elements(self.codomain().some_elements()):
tester.assertEqual(identity(q), q)
def _image_homology(self, g, codomain=None):
r"""
Return the image of the homology class ``g`` under this morphism.
This is a helper method for :meth:`__call__`.
Subclasses can override this method if the morphism is meaningful on
the level of homology.
However, it's usually easier to override :meth:`_image_homology_edge`,
:meth:`_image_homology_gen`, or :meth:`_image_homology_matrix` to
support mapping homology classes.
INPUT:
- ``codomain`` -- a simplicial homology or ``None`` (default:
``None``); if set, the homology where the result should live,
otherwise, the result will live in the :meth:`homology` of the
:meth:`codomain`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
The image of a homology class::
sage: from flatsurf import SimplicialHomology
sage: H = SimplicialHomology(S)
sage: a, b = H.gens()
sage: H.hom(morphism)(a)
B[(0, 1)]
"""
if g.parent().surface() is not self.domain():
raise ValueError("g must be a homology class over this morphism's domain")
if codomain is None:
codomain = self.codomain().homology()
assert (
codomain.surface() is self.codomain()
), "codomain must be a homology of the codomain() of this morphism"
return g.parent().hom(
self._image_homology_matrix(domain=g.parent(), codomain=codomain),
codomain=codomain,
)(g)
def _section_homology(self, h, codomain=None):
r"""
Return a preimage of the homology class ``h`` under this morphism.
This is a helper method for :meth:`__call__` of the :meth:`section`.
Subclasses can override this method if the morphism is meaningful on
the level of homology.
However, it's usually easier to override :meth:`_section_homology_edge`,
:meth:`_section_homology_gen`, or :meth:`_section_homology_matrix` to
support mapping homology classes.
INPUT:
- ``codomain`` -- a simplicial homology or ``None`` (default: ``None``);
if set, the homology where the result should live; otherwise, the
result will live in the :meth:`homology` of the :meth:`domain`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: T = morphism.codomain()
sage: from flatsurf import SimplicialHomology
sage: H = SimplicialHomology(T)
sage: a, b = H.gens()
sage: a
B[(0, 1)]
sage: H.hom(morphism * morphism.section())(a)
B[(0, 1)]
"""
return SurfaceMorphism._image_homology(self.section(), h, codomain=codomain)
def _test_section_homology(self, **options):
r"""
Verify that :meth:`_section_homology` actually produces a
section.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism._test_section_homology()
"""
tester = self._tester(**options)
section = self.section()
identity = self * section
homology = self.codomain().homology()
for q in tester.some_elements(homology.some_elements()):
tester.assertEqual(q.parent().hom(identity)(q), q)
@cached_method
def _image_homology_matrix(self, domain, codomain):
r"""
Return the matrix `M` describing how this morphism acts on homology,
i.e., for a homology class given by a vector `c` with respect to a
basis of homology of the domain, the image is `M c` with respect to the
basis of homology of the codomain.
This is a helper method for :meth:`__call__` and
:meth:`_image_homology`.
Subclasses can override this method if the morphism is meaningful (and
linear) on the level of homology.
However, it is often easier to override :meth:`_image_homology_edge` or
:meth:`_image_homology_gen`.
INPUT:
- ``domain`` -- a simplicial homology over the :meth:`domain`
- ``codomain`` -- a simplicial homology over the :meth:`codomain`
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism._image_homology_matrix(S.homology(), morphism.codomain().homology())
[1 0]
[0 1]
"""
assert domain.surface() is self.domain()
assert codomain.surface() is self.codomain()
domain_gens = domain.gens()
codomain_gens = codomain.gens()
from sage.all import matrix, ZZ
M = matrix(ZZ, len(codomain_gens), len(domain_gens), sparse=True)
for x, domain_gen in enumerate(domain_gens):
image = self._image_homology_gen(domain_gen, codomain=codomain)
for y, codomain_gen in enumerate(codomain_gens):
M[y, x] = image.coefficient(codomain_gen)
M.set_immutable()
return M
def _section_homology_matrix(self, domain, codomain):
r"""
Return the matrix describing a section of this morphism on the level of
homology, see :meth:`_image_homology_matrix`.
INPUT:
- ``domain`` -- a simplicial homology over the :meth:`codomain`
- ``codomain`` -- a simplicial homology over the :meth:`domain`
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism._section_homology_matrix(morphism.codomain().homology(), S.homology())
[1 0]
[0 1]
"""
M = self._image_homology_matrix(domain=codomain, codomain=domain)
if M.rank() != M.nrows():
raise NotImplementedError(
"cannot compute section of homology matrix because map is not onto in homology"
)
return M.pseudoinverse().change_ring(M.base_ring())
def _image_homology_gen(self, gen, codomain):
r"""
Return the image of a generator of homology ``gen``.
This is a helper method for :meth:`__call__` and
:meth:`_image_homology_matrix`.
Subclasses can override this method if the morphism is meaningful (and
linear) on the level of homology.
However, it is often easier to override :meth:`_image_homology_edge` instead.
INPUT:
- ``codomain`` -- a simplicial homology over the :meth:`codomain`
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: from flatsurf import SimplicialHomology
sage: H = SimplicialHomology(S)
sage: a, b = H.gens()
sage: morphism._image_homology_gen(a, codomain=morphism.codomain().homology())
B[(0, 1)]
sage: morphism._image_homology_gen(b, codomain=morphism.codomain().homology())
B[(0, 0)]
"""
assert codomain.surface() is self.codomain()
chain = gen._chain
image = codomain.zero()
for label, edge in chain.support():
coefficient = chain[(label, edge)]
assert coefficient
image += coefficient * self._image_homology_edge(
label, edge, codomain=codomain
)
return codomain(image)
def _section_homology_gen(self, gen, codomain):
r"""
Return a preimage of the homology generator ``gen``.
This is a helper method for :meth:`_image_homology_matrix` of
:meth:`section`. But usually this is not invoked since we compute the
section with linear algebra in :meth:`_section_homology_matrix`.
INPUT:
- ``codomain`` -- a simplicial homology over the :meth:`domain`
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: from flatsurf import SimplicialHomology
sage: H = SimplicialHomology(morphism.codomain())
sage: a, b = H.gens()
sage: morphism._section_homology_gen(a, codomain=S.homology())
B[(0, 1)]
"""
return SurfaceMorphism._image_homology_gen(
self.section(), gen, codomain=codomain
)
def _image_homology_edge(self, label, edge, codomain):
r"""
Return the image of the homology class generated by ``edge`` in the
polygon ``label`` under this morphism.
This is a helper method for :meth:`__call__` and
:meth:`_image_homolyg_gen`.
Subclasses can override this method if the morphism is meaningful (and
linear) on the level of homology.
INPUT:
- ``codomain`` -- a simplicial homology over the :meth:`codomain`
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism._image_homology_edge(0, 0, codomain=morphism.codomain().homology())
B[(0, 0)]
sage: morphism._image_homology_edge(0, 1, codomain=morphism.codomain().homology())
B[(0, 1)]
"""
assert codomain.surface() is self.codomain()
raise NotImplementedError(
f"a {type(self).__name__} cannot compute the image of an edge yet"
)
def _section_homology_edge(self, label, edge, codomain):
r"""
Return a preimage of an edge in homology.
This is a helper method for :meth:`_image_homology_matrix` of
:meth:`section`. But usually this is not invoked since we compute the
section with linear algebra in :meth:`_section_homology_matrix`.
INPUT:
- ``codomain`` -- a simplicial homology over the :meth:`domain`
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: morphism = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: morphism._section_homology_edge(0, 0, codomain=S.homology())
B[(0, 0)]
"""
assert codomain.surface() is self.domain()
domain = self.codomain().homology()
for lab, e in self.domain().edges():
if self._image_homology_edge(lab, e, codomain=domain) == domain(
(label, edge)
):
return codomain((lab, e))
raise NotImplementedError(
"not a single edge maps to this edge, cannot implement preimage of this edge yet"
)
def _composition(self, other):
r"""
Return the composition of this morphism and ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[2, 0], [0, 1]]), in_place=False)
sage: g = f.codomain().apply_matrix(matrix([[1/2, 0], [0, 1]]), in_place=False)
sage: g * f
Composite morphism:
From: Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from a square
Defn: Linear morphism:
From: Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from a rectangle
Defn: [2 0]
[0 1]
then
Linear morphism:
From: Translation Surface in H_1(0) built from a rectangle
To: Translation Surface in H_1(0) built from a square
Defn: [1/2 0]
[ 0 1]
"""
if other.codomain() is not self.domain():
raise ValueError(
f"morphisms cannot be composed because domain of\n{self}\nis not compatible with codomain of\n{other}"
)
if isinstance(other, IdentityMorphism):
return self
if isinstance(self, IdentityMorphism):
return other
return CompositionMorphism._create_morphism(self, other)
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: H = End(S)
sage: H.identity() == H.identity()
True
"""
raise NotImplementedError(
f"{type(self).__name__} does not implement __eq__ yet"
)
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: H = End(S)
sage: hash(H.identity()) == hash(H.identity())
True
"""
raise NotImplementedError(
f"{type(self).__name__} does not implement __hash__ yet"
)
[docs]
class SectionMorphism(SurfaceMorphism):
r"""
The formal section of a morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: morphism = S.subdivide_edges(2)
sage: section = morphism.section()
sage: section
Section morphism:
From: Translation Surface in H_2(2, 0^4) built from a regular octagon with 8 marked vertices
To: Translation Surface in H_2(2) built from a regular octagon
Defn: Section of Edge-Subdivision morphism:
From: Translation Surface in H_2(2) built from a regular octagon
To: Translation Surface in H_2(2, 0^4) built from a regular octagon with 8 marked vertices
TESTS::
sage: from flatsurf.geometry.morphism import SectionMorphism
sage: isinstance(section, SectionMorphism)
True
sage: TestSuite(section).run()
"""
[docs]
def __init__(self, parent, morphism):
super().__init__(parent)
self._morphism = morphism
[docs]
def section(self):
r"""
Return a section of this section.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: morphism = S.subdivide_edges(2)
sage: section = morphism.section()
sage: section.section() == morphism
True
"""
return self._morphism
@classmethod
def _create_morphism(cls, morphism):
r"""
Return a formal section of ``morphism``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: morphism = S.subdivide_edges(2)
sage: from flatsurf.geometry.morphism import SectionMorphism
sage: SectionMorphism._create_morphism(morphism)
Section morphism:
From: Translation Surface in H_2(2, 0^4) built from a regular octagon with 8 marked vertices
To: Translation Surface in H_2(2) built from a regular octagon
Defn: Section of Edge-Subdivision morphism:
From: Translation Surface in H_2(2) built from a regular octagon
To: Translation Surface in H_2(2, 0^4) built from a regular octagon with 8 marked vertices
"""
return super()._create_morphism(
morphism.codomain(), morphism.domain(), morphism
)
def _image_point(self, p):
r"""
Implements :meth:`SurfaceMorphism._image_point`, see
:meth:`SurfaceMorphism._section_point`.
"""
return self._morphism._section_point(p)
def _section_point(self, q):
r"""
Implements :meth:`SurfaceMorphism._section_point`, see
:meth:`SurfaceMorphism._image_point`.
"""
return self._morphism._image_point(q)
def _image_homology(self, g, codomain=None):
r"""
Implements :meth:`SurfaceMorphism._image_homology`, see
:meth:`SurfaceMorphism._section_homology`.
"""
return self._morphism._section_homology(g, codomain=codomain)
def _section_homology(self, h, codomain=None):
r"""
Implements :meth:`SurfaceMorphism._section_homology`, see
:meth:`SurfaceMorphism._image_homology`.
"""
return self._morphism._image_homology(h, codomain=codomain)
def _image_homology_gen(self, gen, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_gen`, see
:meth:`SurfaceMorphism._section_homology_gen`.
"""
assert codomain.surface() is self.codomain()
return self._morphism._section_homology_gen(gen, codomain=codomain)
def _section_homology_gen(self, gen, codomain):
r"""
Implements :meth:`SurfaceMorphism._section_homology_gen`, see
:meth:`SurfaceMorphism._image_homology_gen`.
"""
assert codomain.surface() is self.codomain()
return self._morphism._image_homology_gen(gen, codomain=codomain)
def _image_homology_matrix(self, domain, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_matrix`, see
:meth:`SurfaceMorphism._section_homology_matrix`.
"""
assert domain.surface() is self.domain()
assert codomain.surface() is self.codomain()
return self._morphism._section_homology_matrix(domain=domain, codomain=codomain)
def _section_homology_matrix(self, domain, codomain):
r"""
Implements :meth:`SurfaceMorphism._section_homology_matrix`, see
:meth:`SurfaceMorphism._image_homology_matrix`.
"""
assert domain.surface() is self.codomain()
assert codomain.surface() is self.domain()
return self._morphism._image_homology_matrix(domain=domain, codomain=codomain)
def _image_homology_edge(self, label, edge, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: g = f.section()
sage: g._image_homology_edge((0, 0), 0, codomain=S.homology())
B[(0, 0)]
"""
return self._morphism._section_homology_edge(label, edge, codomain=codomain)
def _section_homology_edge(self, label, edge, codomain):
r"""
Implements :meth:`SurfaceMorphism._section_homology_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: g = f.section()
sage: g._section_homology_edge(0, 0, codomain=f.codomain().homology())
B[((0, 0), 0)]
"""
return self._morphism._image_homology_edge(label, edge, codomain=codomain)
[docs]
def __eq__(self, other):
r"""
Return whether this section is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: f.section() == f.section()
True
"""
if not isinstance(other, SectionMorphism):
return False
return self._morphism == other._morphism
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with
:meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: hash(f.section()) == hash(f.section())
True
"""
return -hash(self._morphism)
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: f.section()
Section morphism: ...
"""
return "Section"
def _repr_defn(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: f.section()
Section morphism:
From: ...
To: ...
Defn: Section of Triangulation morphism:
From: Translation Surface in H_1(0) built from a square
To: Triangulation of Translation Surface in H_1(0) built from a square
"""
return f"Section of {self._morphism}"
[docs]
class CompositionMorphism(SurfaceMorphism):
r"""
The formal composition of two morphisms between surfaces.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: composition = g * f
sage: composition
Composite morphism:
From: Translation Surface in H_2(2) built from a regular octagon
To: Delaunay triangulation of Triangulation of Translation Surface in H_2(2) built from a regular octagon
Defn: Triangulation morphism:
From: Translation Surface in H_2(2) built from a regular octagon
To: Triangulation of Translation Surface in H_2(2) built from a regular octagon
then Delaunay triangulation morphism:
From: Triangulation of Translation Surface in H_2(2) built from a regular octagon
To: Delaunay triangulation of Triangulation of Translation Surface in H_2(2) built from a regular octagon
TESTS::
sage: from flatsurf.geometry.morphism import CompositionMorphism
sage: isinstance(composition, CompositionMorphism)
True
sage: TestSuite(composition).run()
"""
[docs]
def __init__(self, parent, lhs, rhs):
super().__init__(parent)
# The morphisms as they are executed (in chronological order.)
self._morphisms = []
for morphism in [rhs, lhs]:
if isinstance(morphism, CompositionMorphism):
self._morphisms.extend(morphism._morphisms)
else:
self._morphisms.append(morphism)
assert self._morphisms, "morphisms must not be empty"
assert self._morphisms[0].domain() is self.domain()
assert self._morphisms[-1].codomain() is self.codomain()
@classmethod
def _create_morphism(cls, lhs, rhs):
r"""
Create a composition of ``lhs`` to be executed after ``rhs``.
There should be no need to use this method directly, use ``*`` instead.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: from flatsurf.geometry.morphism import CompositionMorphism
sage: CompositionMorphism._create_morphism(g, f) == g * f
True
"""
return super()._create_morphism(rhs.domain(), lhs.codomain(), lhs, rhs)
def _image_point(self, p):
r"""
Evaluate this morphism on the point ``p``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: h = g * f
sage: p = S(0, 0)
sage: q = h(p)
sage: q == g(f(p))
True
"""
for morphism in self._morphisms:
p = morphism._image_point(p)
return p
def _section_point(self, q):
r"""
Return a preimage of the point ``q``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: h = g * f
sage: p = S(0, 0)
sage: q = h(p)
sage: p == h.section()(q)
True
"""
for morphism in self._morphisms[::-1]:
q = morphism._section_point(q)
return q
def _image_homology_matrix(self, domain, codomain):
r"""
Helper method to compute the image of homology under this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: H = S.homology()
sage: h = H.hom(g * f)
sage: h.matrix()
[ 0 0 1 -1]
[ 0 1 0 -1]
[ 0 0 0 1]
[ 1 0 0 -1]
sage: (g * f)._image_homology_matrix(H, g.codomain().homology())
[ 0 0 1 -1]
[ 0 1 0 -1]
[ 0 0 0 1]
[ 1 0 0 -1]
"""
assert domain.surface() is self.domain()
assert codomain.surface() is self.codomain()
matrix = IdentityMorphism._create_morphism(
self.codomain()
)._image_homology_matrix(domain=codomain, codomain=codomain)
for morphism in self._morphisms[:0:-1]:
matrix *= morphism._image_homology_matrix(
domain=morphism.domain().homology(), codomain=codomain
)
codomain = morphism.domain().homology()
matrix *= self._morphisms[0]._image_homology_matrix(
domain=domain, codomain=codomain
)
return matrix
def _image_homology_edge(self, label, edge, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: g._image_homology_edge((0, 0), 0, codomain=g.codomain().homology())
-B[((0, 0), 1)] - B[((0, 1), 1)] - B[((0, 2), 1)] + B[((0, 3), 0)]
"""
return self._image_homology(
self.domain().homology()((label, edge)), codomain=codomain
)
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: g * f
Composite morphism: ...
"""
return "Composite"
def _repr_defn(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: g * f
Composite morphism:
From: ...
To: ...
Defn: Triangulation morphism:
...
then Delaunay triangulation morphism:
...
"""
return "\nthen ".join(str(morphism) for morphism in self._morphisms)
[docs]
@cached_method
def section(self):
r"""
Return a section of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: h = g * f
sage: h.section()
Composite morphism:
From: Delaunay triangulation of Triangulation of Translation Surface in H_2(2) built from a regular octagon
To: Translation Surface in H_2(2) built from a regular octagon
Defn: Section morphism:
From: Delaunay triangulation of Triangulation of Translation Surface in H_2(2) built from a regular octagon
To: Triangulation of Translation Surface in H_2(2) built from a regular octagon
Defn: Section of Delaunay triangulation morphism:
From: Triangulation of Translation Surface in H_2(2) built from a regular octagon
To: Delaunay triangulation of Triangulation of Translation Surface in H_2(2) built from a regular octagon
then Section morphism:
From: Triangulation of Translation Surface in H_2(2) built from a regular octagon
To: Translation Surface in H_2(2) built from a regular octagon
Defn: Section of Triangulation morphism:
From: Translation Surface in H_2(2) built from a regular octagon
To: Triangulation of Translation Surface in H_2(2) built from a regular octagon
"""
from sage.all import prod
return prod(morphism.section() for morphism in self._morphisms)
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: g * f == g * f
True
"""
if not isinstance(other, CompositionMorphism):
return False
return self.parent() == other.parent() and self._morphisms == other._morphisms
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: f = S.triangulate()
sage: T = f.codomain()
sage: g = T.delaunay_triangulate()
sage: hash(g * f) == hash(g * f)
True
"""
return hash(tuple(self._morphisms))
[docs]
class IdentityMorphism(SurfaceMorphism, IdentityMorphism_sage):
r"""
The identity morphism from a surface to itself.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: identity = End(S).identity()
sage: identity
Identity endomorphism of Translation Surface in H_2(2) built from 3 squares
TESTS::
sage: from flatsurf.geometry.morphism import IdentityMorphism
sage: isinstance(identity, IdentityMorphism)
True
sage: TestSuite(identity).run()
This is the neutral element for composition::
sage: triangulation = S.triangulate()
sage: triangulation * identity == triangulation
True
sage: End(triangulation.codomain()).identity() * triangulation == triangulation
True
"""
[docs]
def __init__(self, parent):
if parent.domain() is not parent.codomain():
raise ValueError("domain and codomain of identity must be identical")
super().__init__(parent)
@classmethod
def _create_morphism(cls, domain):
r"""
Return the identity morphism on ``domain``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: from flatsurf.geometry.morphism import IdentityMorphism
sage: f = IdentityMorphism._create_morphism(S)
sage: f == End(S).identity()
True
"""
return super()._create_morphism(domain, domain)
[docs]
def section(self):
r"""
Return an inverse of this morphism, i.e., this morphism itself.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: identity = End(S).identity()
sage: identity.section() == identity
True
"""
return self
def _image_point(self, p):
r"""
Return the image of ``p`` under this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: f = End(S).identity()
sage: f(S(0, 0))
Vertex 0 of polygon 0
"""
return p
def _image_homology_edge(self, label, edge, codomain):
r"""
Helper method to compute the image of homology under this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = End(S).identity()
sage: f._image_homology_edge(0, 0, codomain=S.homology())
B[(0, 0)]
"""
assert codomain.surface() is self.codomain()
return codomain((label, edge))
def _repr_type(self):
r"""
Return a printable representation of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: identity = End(S).identity()
sage: identity
Identity endomorphism of Translation Surface in H_2(2) built from 3 squares
"""
return "Identity"
[docs]
def __reduce__(self):
r"""
Return a serializable version of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: f = End(S).identity()
sage: loads(dumps(f)) == f
True
"""
return (self.parent().identity, ())
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: identity = End(S).identity()
sage: identitz = End(S).identity()
sage: identity == identitz
True
A morphism that is the identity but still distinguishable from the
plain identity::
sage: identitz = S.apply_matrix(matrix([[1, 0], [0, 1]]), in_place=False)
sage: identity == identitz
False
"""
if not isinstance(other, IdentityMorphism):
return False
return self.domain() == other.domain()
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.mcmullen_L(1, 1, 1, 1)
sage: hash(End(S).identity()) == hash(End(S).identity())
True
"""
return hash(self.parent())
[docs]
class SurfaceMorphism_factorization(SurfaceMorphism):
r"""
A morphism between surfaces that is backed by another morphism, usually a
:class:`CompositionMorphism`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f
Delaunay triangulation morphism:
From: Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
sage: f._factorization()
Composite morphism:
From: Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
Defn: Triangulation morphism:
From: Translation Surface in H_1(0) built from a square
To: Triangulation of Translation Surface in H_1(0) built from a square
then Delaunay retriangulation morphism:
From: Triangulation of Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import SurfaceMorphism_factorization
sage: isinstance(f, SurfaceMorphism_factorization)
True
sage: TestSuite(f).run()
"""
def _image_homology(self, g, codomain=None):
r"""
Implements :meth:`SurfaceMorphism._image_homology` by invoking the
underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: a, b = S.homology().gens()
sage: f._image_homology(a)
-B[((0, 0), 0)] - B[((0, 0), 2)]
"""
return self._factorization()._image_homology(g, codomain=codomain)
def _section_homology(self, h, codomain=None):
r"""
Implements :meth:`SurfaceMorphism._section_homology` by invoking the
underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: a, b = f.codomain().homology().gens()
sage: f._section_homology(a)
-B[(0, 0)] - B[(0, 1)]
"""
return self._factorization()._section_homology(h, codomain=codomain)
def _image_homology_matrix(self, domain, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_matrix` by invoking
the underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f._image_homology_matrix(S.homology(), f.codomain().homology())
[-1 0]
[-1 1]
"""
assert domain.surface() is self.domain()
assert codomain.surface() is self.codomain()
return self._factorization()._image_homology_matrix(
domain=domain, codomain=codomain
)
def _section_homology_matrix(self, domain, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_matrix` by invoking
the underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f._section_homology_matrix(f.codomain().homology(), S.homology())
[-1 0]
[-1 1]
"""
assert domain.surface() is self.codomain()
assert codomain.surface() is self.domain()
return self._factorization()._section_homology_matrix(
domain=domain, codomain=codomain
)
def _image_homology_gen(self, gen, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_gen` by invoking the
underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: a, b = S.homology().gens()
sage: f._image_homology_gen(a, codomain=f.codomain().homology())
-B[((0, 0), 0)] - B[((0, 0), 2)]
"""
assert codomain.surface() is self.codomain()
return self._factorization()._image_homology_gen(gen, codomain=codomain)
def _section_homology_gen(self, gen, codomain):
r"""
Implements :meth:`SurfaceMorphism._section_homology_gen` by invoking the
underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: a, b = f.codomain().homology().gens()
sage: f._section_homology_gen(a, codomain=S.homology())
-B[(0, 0)] - B[(0, 1)]
"""
assert codomain.surface() is self.domain()
return self._factorization()._section_homology_gen(gen, codomain=codomain)
def _image_homology_edge(self, label, edge, codomain):
r"""
Implement :meth:`SurfaceMorphism._image_homology_edge` by invoking the
underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f._image_homology_edge(0, 0, codomain=f.codomain().homology())
B[((0, 0), 0)]
"""
assert codomain.surface() is self.codomain()
return self._factorization()._image_homology_edge(label, edge, codomain)
def _section_homology_edge(self, label, edge, codomain):
r"""
Implement :meth:`SurfaceMorphism._section_homology_edge` by invoking the
underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f._section_homology_edge((0, 0), 0, codomain=f.domain().homology())
B[(0, 0)]
"""
assert codomain.surface() is self.domain()
return self._factorization()._section_homology_edge(label, edge, codomain)
def _image_point(self, p):
r"""
Return the image of a point under this morphism by invoking the
underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f(S(0, 0))
Vertex 0 of polygon (0, 0)
"""
return self._factorization()._image_point(p)
def _section_point(self, q):
r"""
Return a preimage of a point under this morphism by determining a
preimage of the underlying morphism of this factorization.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f._section_point(f.codomain()((0, 0), 0))
Vertex 0 of polygon 0
"""
return self._factorization()._section_point(q)
[docs]
def _factorization(self):
r"""
Return the morphism underlying this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f._factorization()
Composite morphism:
From: Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
Defn: Triangulation morphism:
From: Translation Surface in H_1(0) built from a square
To: Triangulation of Translation Surface in H_1(0) built from a square
then Delaunay retriangulation morphism:
From: Triangulation of Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
"""
raise NotImplementedError(
"this factorization morphism is not functional because it does not implement factorization()"
)
def _test_factorization(self, **options):
r"""
Verify that :meth:`_factorization` has been implemented correctly.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()
sage: f._test_factorization()
"""
tester = self._tester(**options)
tester.assertTrue(self.domain() is self._factorization().domain())
tester.assertTrue(self.codomain() is self._factorization().codomain())
[docs]
class NamedUnknownMorphism(SurfaceMorphism):
r"""
A morphism that is not functional, typically a placeholder for
functionality that has not been implemented yet.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = MutableOrientedSimilaritySurface.from_surface(translation_surfaces.square_torus())
sage: f = S.triangulate()
sage: f
Triangulation morphism:
From: Unknown Surface
To: Triangulation of Translation Surface in H_1(0) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import NamedUnknownMorphism
sage: isinstance(f, NamedUnknownMorphism)
True
sage: TestSuite(f).run()
"""
[docs]
def __init__(self, parent, name):
super().__init__(parent)
self._name = name
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = MutableOrientedSimilaritySurface.from_surface(translation_surfaces.square_torus())
sage: S.triangulate()
Triangulation morphism:
From: ...
To: ...
"""
return self._name
def _test_section_point(self, **options):
r"""
Do not test whether this implements :meth:`_section_point` correctly.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = MutableOrientedSimilaritySurface.from_surface(translation_surfaces.square_torus())
sage: f = S.triangulate()
sage: f._test_section_point()
"""
def _test_section_homology(self, **options):
r"""
Do not test whether this implements :meth:`_section_homology` correctly.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = MutableOrientedSimilaritySurface.from_surface(translation_surfaces.square_torus())
sage: f = S.triangulate()
sage: f._test_section_homology()
"""
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = MutableOrientedSimilaritySurface.from_surface(translation_surfaces.square_torus())
sage: S.triangulate() == S.triangulate()
True
"""
if not isinstance(other, NamedUnknownMorphism):
return False
return self.parent() == other.parent() and self._name == other._name
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = MutableOrientedSimilaritySurface.from_surface(translation_surfaces.square_torus())
sage: hash(S.triangulate()) == hash(S.triangulate())
True
"""
return hash((self.parent(), self._name))
[docs]
def __reduce__(self):
r"""
Return a serializable version of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = MutableOrientedSimilaritySurface.from_surface(translation_surfaces.square_torus())
sage: loads(dumps(S.triangulate())) == S.triangulate()
True
"""
return unpickle_NamedUnknownMorphism, (
self.domain(),
self.codomain(),
self._name,
)
[docs]
def unpickle_NamedUnknownMorphism(*args):
r"""
Unpickle a :class:`NamedUnknownMorphism`.
This works around a bug in SageMath 9.8 which fails to unpickle through
``NamedUnknownMorphism._create_morphism`` directly with: ``AttributeError:
type object 'sage.misc.inherit_comparison.InheritComparisonMeta' has no
attribute '_create_morphism'``
EXAMPLES::
sage: from flatsurf import translation_surfaces, MutableOrientedSimilaritySurface
sage: S = MutableOrientedSimilaritySurface.from_surface(translation_surfaces.square_torus())
sage: loads(dumps(S.triangulate())) == S.triangulate()
True
"""
return NamedUnknownMorphism._create_morphism(*args)
[docs]
class NamedFactorizationMorphism(SurfaceMorphism_factorization):
r"""
A morphism that is implement by another morphism but has a more appealing
name when printing.
This is commonly used when implementing new morphisms that rely on a
sequence of existing morphisms while providing a nice interface to the user
of sage-flatsurf.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: g = f.codomain().apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: from flatsurf.geometry.morphism import NamedFactorizationMorphism
sage: h = NamedFactorizationMorphism._create_morphism(S, g.codomain(), "Foo", g * f)
sage: h
Foo morphism:
From: Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from 2 triangles
TESTS::
sage: from flatsurf.geometry.morphism import NamedFactorizationMorphism
sage: isinstance(h, NamedFactorizationMorphism)
True
sage: TestSuite(h).run()
"""
[docs]
def __init__(self, parent, name, factorization):
super().__init__(parent)
self._name = name
self.__factorization = factorization
if self._factorization().domain() is not self.domain():
raise ValueError("factorization must start at the domain of the morphism")
if self._factorization().codomain() is not self.codomain():
raise ValueError("factorization must end at the codomain of the morphism")
def _repr_type(self):
r"""
Helper method for :meth;`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: g = f.codomain().apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: from flatsurf.geometry.morphism import NamedFactorizationMorphism
sage: h = NamedFactorizationMorphism._create_morphism(S, g.codomain(), "Foo", g * f)
sage: h
Foo morphism:
...
"""
return self._name
[docs]
def _factorization(self):
r"""
Return the morphism underlying this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: g = f.codomain().apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: from flatsurf.geometry.morphism import NamedFactorizationMorphism
sage: h = NamedFactorizationMorphism._create_morphism(S, g.codomain(), "Foo", g * f)
sage: h._factorization()
Composite morphism:
From: Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from 2 triangles
Defn: Triangulation morphism:
From: Translation Surface in H_1(0) built from a square
To: Triangulation of Translation Surface in H_1(0) built from a square
then Linear morphism:
From: Triangulation of Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from 2 triangles
Defn: [1 2]
[0 1]
"""
return self.__factorization
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: g = f.codomain().apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: from flatsurf.geometry.morphism import NamedFactorizationMorphism
sage: h0 = NamedFactorizationMorphism._create_morphism(S, g.codomain(), "Foo", g * f)
sage: h1 = NamedFactorizationMorphism._create_morphism(S, g.codomain(), "Foo", g * f)
sage: h0 == h1
True
"""
if not isinstance(other, NamedFactorizationMorphism):
return False
return (
self.__factorization == other.__factorization and self._name == other._name
)
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: g = f.codomain().apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: from flatsurf.geometry.morphism import NamedFactorizationMorphism
sage: h0 = NamedFactorizationMorphism._create_morphism(S, g.codomain(), "Foo", g * f)
sage: h1 = NamedFactorizationMorphism._create_morphism(S, g.codomain(), "Foo", g * f)
sage: hash(h0) == hash(h1)
True
"""
return hash((self.__factorization, self._name))
[docs]
class TriangulationMorphism_base(SurfaceMorphism):
r"""
Abstract base class for morphisms from a surface to its triangulation.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: G = SymmetricGroup(4)
sage: S = translation_surfaces.origami(G('(1,2,3,4)'), G('(1,4,2,3)'))
sage: f = S.triangulate()
sage: f
Triangulation morphism:
From: Origami defined by r=(1,2,3,4) and u=(1,4,2,3)
To: Triangulation of Origami defined by r=(1,2,3,4) and u=(1,4,2,3)
TESTS::
sage: from flatsurf.geometry.morphism import TriangulationMorphism_base
sage: isinstance(f, TriangulationMorphism_base)
True
sage: TestSuite(f).run()
"""
def _image_edge(self, label, edge):
r"""
Return the image of the ``edge`` of the polygon with ``label`` in the
codomain of this triangulation.
Subclasses must implement this method to make this morphism functional.
Since this is a triangulation, all edges of the domain are preserved in
the codomain.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: G = SymmetricGroup(4)
sage: S = translation_surfaces.origami(G('(1,2,3,4)'), G('(1,4,2,3)'))
sage: f = S.triangulate()
sage: f._image_edge(1, 0)
((1, 0), 0)
"""
raise NotImplementedError(
"this triangulation morphism is not functional because it does not implement _image_edge() yet"
)
def _section_edge(self, label, edge):
r"""
Return a preimage of the ``edge`` of the polygon with ``label`` in the
domain of this triangulation.
If the ``edge`` did not exist already in the domain, returns only the
label of polygon but ``None`` for the edge.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: G = SymmetricGroup(4)
sage: S = translation_surfaces.origami(G('(1,2,3,4)'), G('(1,4,2,3)'))
sage: f = S.triangulate()
sage: f._section_edge((1, 0), 0)
(1, 0)
sage: f._section_edge((1, 0), 1)
(1, 1)
sage: f._section_edge((1, 0), 2)
(1, None)
"""
for preimage_label in self.domain().labels():
for e in range(len(self.domain().polygon(preimage_label).edges())):
if self._image_edge(preimage_label, e) == (label, edge):
return preimage_label, e
for e in range(len(self.domain().polygon(preimage_label).edges())):
if self._image_edge(preimage_label, e)[0] == label:
return preimage_label, None
assert False, "triangle must come from a polygon before triangulation"
def _image_homology_edge(self, label, edge, codomain):
r"""
Implements :class:`SurfaceMorphism._image_homology_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: G = SymmetricGroup(4)
sage: S = translation_surfaces.origami(G('(1,2,3,4)'), G('(1,4,2,3)'))
sage: triangulation = S.triangulate()
sage: triangulation._image_homology_edge(1, 0, codomain=triangulation.codomain().homology())
B[((1, 0), 0)]
"""
assert codomain.surface() is self.codomain()
return codomain(self._image_edge(label, edge))
def _image_point(self, p):
r"""
Implements :meth:`SurfaceMorphism._image_point`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: G = SymmetricGroup(4)
sage: S = translation_surfaces.origami(G('(1,2,3,4)'), G('(1,4,2,3)'))
sage: triangulation = S.triangulate()
sage: triangulation._image_point(S(1, 0))
Vertex 0 of polygon (1, 0)
sage: triangulation._image_point(S(1, (1/2, 1/2)))
Point (1/2, 1/2) of polygon (1, 0)
"""
preimage_label, preimage_coordinates = p.representative()
preimage_polygon = self.domain().polygon(preimage_label)
for preimage_edge in range(len(preimage_polygon.edges())):
relative_coordinates = preimage_coordinates - preimage_polygon.vertex(
preimage_edge
)
image_label, image_edge = self._image_edge(preimage_label, preimage_edge)
image_polygon = self.codomain().polygon(image_label)
image_coordinates = image_polygon.vertex(image_edge) + relative_coordinates
if image_polygon.contains_point(image_coordinates):
return self.codomain()(image_label, image_coordinates)
assert (
False
), "point must be in one of the polygons that split up the original polygon"
def _section_point(self, q):
r"""
Implements :meth:`SurfaceMorphism._section_point`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: G = SymmetricGroup(4)
sage: S = translation_surfaces.origami(G('(1,2,3,4)'), G('(1,4,2,3)'))
sage: triangulation = S.triangulate()
sage: p = S(1, 0)
sage: q = triangulation._image_point(p)
sage: p == triangulation._section_point(q)
True
sage: p = S(1, (1/2, 1/2))
sage: q = triangulation._image_point(p)
sage: p == triangulation._section_point(q)
True
"""
image_label, image_coordinates = q.representative()
image_polygon = self.codomain().polygon(image_label)
for image_edge in range(len(image_polygon.edges())):
relative_coordinates = image_coordinates - image_polygon.vertex(image_edge)
preimage_label, preimage_edge = self._section_edge(image_label, image_edge)
if preimage_edge is None:
continue
preimage_polygon = self.domain().polygon(preimage_label)
preimage_coordinates = (
preimage_polygon.vertex(preimage_edge) + relative_coordinates
)
assert preimage_polygon.contains_point(
preimage_coordinates
), "point must be contained in the polygon before triangulation"
return self.domain()(preimage_label, preimage_coordinates)
assert (
False
), "point must be in the polygon from which the triangulation originated"
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: G = SymmetricGroup(4)
sage: S = translation_surfaces.origami(G('(1,2,3,4)'), G('(1,4,2,3)'))
sage: f = S.triangulate()
sage: f
Triangulation morphism:
...
"""
return "Triangulation"
[docs]
class TriangulationMorphism_LazyTriangulatedSurface(TriangulationMorphism_base):
r"""
A triangulation that maps a surface into a class :class:`~flatsurf.geometry.lazy.LazyTriangulatedSurface`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: f
Triangulation morphism:
From: Translation Surface in H_1(0) built from a square
To: Triangulation of Translation Surface in H_1(0) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import TriangulationMorphism_LazyTriangulatedSurface
sage: isinstance(f, TriangulationMorphism_LazyTriangulatedSurface)
True
sage: TestSuite(f).run()
.. SEEALSO::
:meth:`flatsurf.geometry.categories.similarity_surfaces.SimilaritySurfaces.Oriented.ParentMethods.triangulate`
"""
def _image_edge(self, label, edge):
r"""
Implements :meth:`TriangulationMorphism_base._image_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.triangulate()
sage: f._image_edge(0, 0)
((0, 0), 0)
"""
return self.codomain()._image(label)[1][edge]
[docs]
def __eq__(self, other):
r"""
Return whether this triangulation is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: S.triangulate() == S.triangulate()
True
"""
if not isinstance(other, TriangulationMorphism_LazyTriangulatedSurface):
return False
return self.parent() == other.parent()
[docs]
def __hash__(self):
r"""
Return a hash value for this triangulation that is compatible with
:meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: hash(S.triangulate()) == hash(S.triangulate())
True
"""
return hash(self.parent())
[docs]
class DelaunayTriangulationMorphism_delaunay_decomposition(TriangulationMorphism_base):
r"""
A triangulation that maps a a Delaunay decomposition into the Delaunay
triangulation from which it was created.
This morphism is used internally in
:meth:`~flatsurf.geometry.categories.similarity_surfaces.SimilaritySurfaces.Oriented.ParentMethods.delaunay_decompose`,
the actual
delaunay decomposition, is the inverse of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_decompose()._factorization()._morphisms[1].section()
sage: f
Triangulation morphism:
From: Delaunay cell decomposition of Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import DelaunayTriangulationMorphism_delaunay_decomposition
sage: isinstance(f, DelaunayTriangulationMorphism_delaunay_decomposition)
True
sage: TestSuite(f).run()
.. SEEALSO::
:meth:`flatsurf.geometry.categories.similarity_surfaces.SimilaritySurfaces.Oriented.ParentMethods.delaunay_decompose`,
"""
def _image_edge(self, label, edge):
r"""
Implements :meth:`TriangulationMorphism_base._image_edge.`
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_decompose()._factorization()._morphisms[1].section()
sage: f._image_edge((0, 0), 0)
((0, 0), 0)
"""
_, edges = self.domain()._cell(label)
return edges[edge]
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_decompose()._factorization()._morphisms[1].section()
sage: g = S.delaunay_decompose()._factorization()._morphisms[1].section()
sage: f == g
True
"""
if not isinstance(other, DelaunayTriangulationMorphism_delaunay_decomposition):
return False
return self.parent() == other.parent()
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with
:meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_decompose()._factorization()._morphisms[1].section()
sage: g = S.delaunay_decompose()._factorization()._morphisms[1].section()
sage: hash(f) == hash(g)
True
"""
return hash(self.parent())
[docs]
class DelaunayTriangulationMorphism(SurfaceMorphism):
r"""
A morphism from a triangulated surface to its Delaunay triangulation.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()._factorization()._morphisms[1]
sage: f
Delaunay retriangulation morphism:
From: Triangulation of Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import DelaunayTriangulationMorphism
sage: isinstance(f, DelaunayTriangulationMorphism)
True
sage: TestSuite(f).run()
.. SEEALSO::
:meth:`flatsurf.geometry.categories.similarity_surfaces.SimilaritySurfaces.Oriented.ParentMethods.delaunay_triangulate`
"""
def _image_homology_edge(self, label, edge, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()._factorization()._morphisms[1]
sage: f._image_homology_edge((0, 0), 0, codomain=f.codomain().homology())
B[((0, 0), 0)]
"""
gens, chain_matrix = self._image_homology_edge_chain_matrix()
image = chain_matrix.column(gens.index((label, edge)))
return sum(
c * codomain(gens[i])
for (i, c) in zip(image.support(), image.coefficients())
)
@cached_method
def _image_homology_edge_chain_matrix(self):
r"""
Return the matrix that describes the action of this morphism in
homology on the generators of the chain module.
Helper method for :meth:`_image_homology_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()._factorization()._morphisms[1]
sage: gens, matrix = f._image_homology_edge_chain_matrix()
sage: gens
(((0, 0), 0), ((0, 0), 1), ((0, 0), 2), ((0, 1), 0), ((0, 1), 1), ((0, 1), 2))
sage: matrix
[1 0 0 0 0 0]
[0 1 0 0 0 0]
[0 0 1 0 0 0]
[0 0 0 1 0 0]
[0 0 0 0 1 0]
[0 0 0 0 0 1]
"""
for label in self.codomain().labels():
self.codomain()._certify(label)
gens = tuple(self.domain().edges())
from sage.all import identity_matrix, ZZ
chain_matrix = identity_matrix(ZZ, len(gens), sparse=True)
for flip in self.codomain()._flips[::-1]:
chain_matrix *= self._image_homology_edge_chain_matrix_flip(flip, gens)
return gens, chain_matrix
def _image_homology_edge_chain_matrix_flip(self, flip, gens):
r"""
Return the matrix that describes the action of a single ``flip`` on
homology on the generators ``gens`` of the chain module.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()._factorization()._morphisms[1]
sage: T = f.domain()
sage: f._image_homology_edge_chain_matrix_flip((((0, 0), 1), ((0, 0), 3)), tuple(T.edges()))
[0 1 1 0 0 0]
[0 0 0 0 0 0]
[1 1 0 0 0 0]
[0 0 0 1 0 0]
[0 0 0 0 1 0]
[0 0 0 0 0 1]
TESTS:
This method should be migrated into the morphism describing a triangle
flip but currently there is no such morphism::
sage: from flatsurf.geometry.morphism import SurfaceMorphism
sage: isinstance(T.triangle_flip((0, 0), 1), SurfaceMorphism)
False
"""
from sage.all import zero_matrix, ZZ
(label, edge), (opposite_label, opposite_edge) = flip
matrix = zero_matrix(ZZ, len(gens), sparse=True)
for i, (lbl, e) in enumerate(gens):
if lbl != label and lbl != opposite_label:
matrix[i, i] = 1
continue
def image(preimage, *images):
def denormalize(lbl, e):
if lbl == label:
return lbl, (e + edge) % 3
if lbl == opposite_label:
return lbl, (e + opposite_edge) % 3
assert False
preimage = denormalize(*preimage)
for image in images:
image = denormalize(*image)
matrix[gens.index(image), gens.index(preimage)] = 1
image((label, 0), (opposite_label, 1), (label, 2))
image((label, 1), (opposite_label, 2))
image((label, 2), (label, 1))
image((opposite_label, 0), (label, 1), (opposite_label, 2))
image((opposite_label, 1), (label, 2))
image((opposite_label, 2), (opposite_label, 1))
return matrix
def _image_point(self, p):
r"""
Return the image of ``p`` under this retriangulation.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon().triangulate().codomain()
sage: g = S.delaunay_triangulate()
sage: p = S((0, 0), 0)
sage: g(p)
Vertex 0 of polygon (0, 0)
This is not implemented in non-trivial cases yet; the most reasonable
way to do this, seems to be to track the point in a mutable surface
while flipping the edges again::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.cathedral(1, 1).triangulate().codomain()
sage: g = S.delaunay_triangulate()
sage: p = S((0, 0), 0)
sage: g(p)
Traceback (most recent call last):
...
NotImplementedError: Delaunay retriangulation cannot map points in non-trivial cases yet
"""
for flip in self._flips():
raise NotImplementedError(
"Delaunay retriangulation cannot map points in non-trivial cases yet"
)
return self.codomain()(*p.representative())
def _section_point(self, q):
r"""
Return the preimage of ``q`` under this retriangulation.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon().triangulate().codomain()
sage: g = S.delaunay_triangulate()
sage: p = S((0, 0), 0)
sage: q = g(p)
sage: g.section()(q) == p
True
This is not implemented in non-trivial cases yet; the most reasonable
way to do this, seems to be to track the point in a mutable surface
while unflipping the edges::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.cathedral(1, 1).triangulate().codomain()
sage: g = S.delaunay_triangulate()
sage: q = g.codomain()((0, 0), 0)
sage: g.section()(q)
Traceback (most recent call last):
...
NotImplementedError: Delaunay retriangulation cannot pull back points in non-trivial cases yet
"""
for flip in self._flips()[::-1]:
raise NotImplementedError(
"Delaunay retriangulation cannot pull back points in non-trivial cases yet"
)
return self.domain()(*q.representative())
def _flips(self):
r"""
Return the sequence of flips performed by this retriangulation.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.cathedral(1, 1).triangulate().codomain()
sage: g = S.delaunay_triangulate()
sage: f = g._factorization()._morphisms[1]
sage: f._flips()
[(((1, 7), 0), ((1, 5), 2)),
(((1, 7), 2), ((1, 4), 2)),
(((3, 2), 0), ((3, 1), 2)),
(((3, 2), 1), ((3, 3), 0)),
(((3, 3), 1), ((3, 4), 0)),
(((3, 0), 2), ((3, 4), 2)),
(((1, 5), 1), ((1, 6), 2)),
(((1, 0), 2), ((1, 1), 0))]
"""
for label in self.codomain().labels():
self.codomain()._certify(label)
return self.codomain()._flips
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.cathedral(1, 1).triangulate().codomain()
sage: g = S.delaunay_triangulate()
sage: f = g._factorization()._morphisms[1]
sage: f
Delaunay retriangulation morphism:
...
"""
return "Delaunay retriangulation"
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()._factorization()._morphisms[1]
sage: g = S.delaunay_triangulate()._factorization()._morphisms[1]
sage: f == g
True
"""
if not isinstance(other, DelaunayTriangulationMorphism):
return False
return self.parent() == other.parent()
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_triangulate()._factorization()._morphisms[1]
sage: g = S.delaunay_triangulate()._factorization()._morphisms[1]
sage: hash(f) == hash(g)
True
"""
return hash(self.parent())
[docs]
class DelaunayDecompositionMorphism(SectionMorphism):
r"""
A morphism describing the Delaunay decomposition of a Delaunay triangulation.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_decompose()._factorization()._morphisms[1]
sage: f
Delaunay decomposition morphism:
From: Delaunay triangulation of Translation Surface in H_1(0) built from a square
To: Delaunay cell decomposition of Translation Surface in H_1(0) built from a square
Defn: Section of Triangulation morphism:
From: Delaunay cell decomposition of Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
This morphism is implemented as the formal section of a triangulation
morphism::
sage: f.section()
Triangulation morphism:
From: Delaunay cell decomposition of Translation Surface in H_1(0) built from a square
To: Delaunay triangulation of Translation Surface in H_1(0) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import DelaunayDecompositionMorphism
sage: isinstance(f, DelaunayDecompositionMorphism)
True
sage: TestSuite(f).run()
.. SEEALSO::
:meth:`flatsurf.geometry.categories.similarity_surfaces.SimilaritySurfaces.Oriented.ParentMethods.delaunay_decompose`
"""
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_decompose()._factorization()._morphisms[1]
sage: f
Delaunay decomposition morphism:
...
"""
return "Delaunay decomposition"
@classmethod
def _create_morphism(cls, domain, codomain):
r"""
Return a morphism from ``domain`` to ``codomain``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus().delaunay_triangulate().codomain()
sage: T = S.delaunay_decompose().codomain()
sage: from flatsurf.geometry.morphism import DelaunayDecompositionMorphism
sage: f = DelaunayDecompositionMorphism._create_morphism(S, T)
"""
return super()._create_morphism(
DelaunayTriangulationMorphism_delaunay_decomposition._create_morphism(
codomain, domain
)
)
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_decompose()._factorization()._morphisms[1]
sage: g = S.delaunay_decompose()._factorization()._morphisms[1]
sage: f == g
True
"""
if not isinstance(other, DelaunayDecompositionMorphism):
return False
return self.parent() == other.parent()
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.delaunay_decompose()._factorization()._morphisms[1]
sage: g = S.delaunay_decompose()._factorization()._morphisms[1]
sage: hash(f) == hash(g)
True
"""
return hash(self.parent())
[docs]
class DelaunayDecompositionIsomorphism(SurfaceMorphism_factorization):
r"""
An isomorphism between Delaunay decompositions.
.. NOTE::
This method relies on pyflatsurf to figure out the isomorphism when
:meth:`_factorization` is called. This is not a
:class:`NamedFactorizationMorphism` since the factorization is not
pickleable currently. This is not a very pretty solution since the
exact chosen isomorphism is now an implementation detail that could
change between different versions of libflatsurf.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: T = S.relabel({0: 1})
sage: isomorphism = S.delaunay_decompose(codomain=T)._factorization() # optional: pyflatsurf # random output due to cppyy deprecation warnings
sage: isomorphism # optional: pyflatsurf
Delaunay decomposition morphism:
From: Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import DelaunayDecompositionIsomorphism
sage: isinstance(isomorphism, DelaunayDecompositionIsomorphism) # optional: pyflatsurf
True
sage: TestSuite(isomorphism).run() # optional: pyflatsurf
.. SEEALSO::
:meth:`flatsurf.geometry.categories.similarity_surfaces.SimilaritySurfaces.Oriented.ParentMethods.delaunay_decompose`
"""
[docs]
@cached_method
def _factorization(self):
r"""
Return the sequence of morphism that implement this isomorphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: T = S.relabel({0: 1})
sage: isomorphism = S.delaunay_decompose(codomain=T)._factorization() # optional: pyflatsurf
sage: isomorphism._factorization() # optional: pyflatsurf
Composite morphism:
From: Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from a square
Defn: Triangulation morphism:
From: Translation Surface in H_1(0) built from a square
To: Triangulation of Translation Surface in H_1(0) built from a square
then pyflatsurf conversion morphism:
From: Triangulation of Translation Surface in H_1(0) built from a square
To: Surface backed by FlatTriangulationCombinatorial...
then pyflatsurf deformation morphism:
From: Surface backed by FlatTriangulationCombinatorial...
To: Surface backed by FlatTriangulationCombinatorial...
Defn: ...
then pyflatsurf reconversion morphism:
From: Surface backed by FlatTriangulationCombinatorial...
To: Triangulation of Translation Surface in H_1(0) built from a square
then Section morphism:
From: Triangulation of Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from a square
Defn: Section of Triangulation morphism:
From: Translation Surface in H_1(0) built from a square
To: Triangulation of Translation Surface in H_1(0) built from a square
"""
from flatsurf.geometry.pyflatsurf.surface import Surface_pyflatsurf
domain_to_pyflatsurf = Surface_pyflatsurf._from_flatsurf(self.domain())
codomain_to_pyflatsurf = Surface_pyflatsurf._from_flatsurf(self.codomain())
from pyflatsurf import flatsurf
deformation = (
domain_to_pyflatsurf.codomain()
.flat_triangulation()
.isomorphism(
codomain_to_pyflatsurf.codomain().flat_triangulation(),
flatsurf.ISOMORPHISM.DELAUNAY_CELLS,
)
.value()
)
from flatsurf.geometry.pyflatsurf.morphism import Morphism_Deformation
return (
codomain_to_pyflatsurf.section()
* Morphism_Deformation._create_morphism(
domain_to_pyflatsurf.codomain(),
codomain_to_pyflatsurf.codomain(),
deformation,
)
* domain_to_pyflatsurf
)
[docs]
def __reduce__(self):
r"""
Return a picklable version of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: T = S.relabel({0: 1})
sage: isomorphism = S.delaunay_decompose(codomain=T)._factorization() # optional: pyflatsurf
sage: loads(dumps(isomorphism)) == isomorphism # optional: pyflatsurf
True
"""
return DelaunayDecompositionIsomorphism, (self.domain(), self.codomain())
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: T = S.relabel({0: 1})
sage: isomorphism = S.delaunay_decompose(codomain=T)._factorization() # optional: pyflatsurf
sage: isomorphism # optional: pyflatsurf
Delaunay decomposition morphism:
...
"""
return "Delaunay decomposition"
def _test_section_point(self, **options):
r"""
Do not test whether :meth:`_section_point` has been implemented correctly.
Currently, points cannot be represented in pyflatsurf backed surfaces
yet, so we disable this test.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: T = S.relabel({0: 1})
sage: isomorphism = S.delaunay_decompose(codomain=T)._factorization() # optional: pyflatsurf
sage: isomorphism._test_section_point() # optional: pyflatsurf
"""
[docs]
def __eq__(self, other):
r"""
Return whether this isomorphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: T = S.relabel({0: 1})
sage: S.delaunay_decompose(codomain=T)._factorization() == S.delaunay_decompose(codomain=T)._factorization() # optional: pyflatsurf
True
"""
if not isinstance(other, DelaunayDecompositionIsomorphism):
return False
return self.parent() == other.parent()
[docs]
def __hash__(self):
r"""
Return a hash value for this isomorphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: T = S.relabel({0: 1})
sage: hash(S.delaunay_decompose(codomain=T)._factorization()) == hash(S.delaunay_decompose(codomain=T)._factorization()) # optional: pyflatsurf
True
"""
return hash(self.parent())
[docs]
class GL2RMorphism(SurfaceMorphism):
r"""
A morphism that describes the application of a matrix in `GL_2(\mathbb{R})`
on each polygon of a surface.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: f
Linear morphism:
From: Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0) built from a quadrilateral
Defn: [1 2]
[0 1]
TESTS::
sage: from flatsurf.geometry.morphism import GL2RMorphism
sage: isinstance(f, GL2RMorphism)
True
sage: TestSuite(f).run()
.. SEEALSO::
:meth:`flatsurf.geometry.categories.similarity_surfaces.SimilaritySurfaces.ParentMethods.apply_matrix`
"""
[docs]
def __init__(self, parent, m):
super().__init__(parent)
from sage.all import matrix
self._matrix = matrix(self.domain().base_ring(), m, immutable=True)
[docs]
def section(self):
r"""
Return an inverse of this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: f.section()
Linear morphism:
From: Translation Surface in H_1(0) built from a quadrilateral
To: Translation Surface in H_1(0) built from a square
Defn: [ 1 -2]
[ 0 1]
"""
return self._create_morphism(self.codomain(), self.domain(), ~self._matrix)
def _image_point(self, p):
r"""
Return the image of the ``point`` under this morphism.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: f(S(0, 0))
Vertex 0 of polygon 0
"""
label, coordinates = p.representative()
return self.codomain()(label, self._matrix * coordinates)
def _section_point(self, q):
return self.section()._image_point(q)
def _image_homology_edge(self, label, edge, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: f._image_homology_edge(0, 0, codomain=f.codomain().homology())
B[(0, 0)]
"""
assert codomain.surface() is self.codomain()
return codomain((label, edge))
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: f
Linear morphism:
...
"""
return "Linear"
def _repr_defn(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: f
Linear morphism:
From: ...
To: ...
Defn: [1 2]
[0 1]
"""
return repr(self._matrix)
[docs]
def __eq__(self, other):
r"""
Return whether this morphis is indistinguishable from ``other``
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: g = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: f == g
True
"""
if not isinstance(other, GL2RMorphism):
return False
return self.parent() == other.parent() and self._matrix == other._matrix
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: g = S.apply_matrix(matrix([[1, 2], [0, 1]]), in_place=False)
sage: hash(f) == hash(g)
True
"""
return hash(self._matrix)
[docs]
class SubdivideEdgesMorphism(SurfaceMorphism):
r"""
A morphism that inserts marked points on edges.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.square_torus()
sage: f = S.subdivide_edges()
sage: f
Edge-Subdivision morphism:
From: Translation Surface in H_1(0) built from a square
To: Translation Surface in H_1(0^3) built from a square
TESTS::
sage: from flatsurf.geometry.morphism import SubdivideEdgesMorphism
sage: isinstance(f, SubdivideEdgesMorphism)
True
sage: TestSuite(f).run()
.. SEEALSO::
:meth:`flatsurf.geometry.categories.similarity_surfaces.SimilaritySurfaces.Oriented.ParentMethods.subdivide_edges`
"""
[docs]
def __init__(self, parent, parts):
super().__init__(parent)
self._parts = parts
def _image_point(self, p):
r"""
Return the image of ``p`` in the codomain of this surface.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: morphism = S.subdivide_edges(2)
sage: from flatsurf.geometry.surface_objects import SurfacePoint
sage: p = SurfacePoint(S, 0, (1, 1))
sage: morphism._image_point(p)
Point (1, 1) of polygon 0
"""
return self.codomain()(*p.representative())
def _section_point(self, q):
r"""
Implements :meth:`SurfaceMorphism._section_point`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: morphism = S.subdivide_edges(2)
sage: p = S(0, (1, 1))
sage: q = morphism(p)
sage: p == morphism.section()(q)
True
"""
return self.domain()(*q.representative())
def _image_homology_edge(self, label, edge, codomain):
r"""
Implements :meth:`SurfaceMorphism._image_homology_edge`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: morphism = S.subdivide_edges(2)
sage: morphism._image_homology_edge(0, 0, codomain=morphism.codomain().homology())
B[(0, 0)] + B[(0, 1)]
"""
return sum(
codomain((label, edge * self._parts + p)) for p in range(self._parts)
)
def _repr_type(self):
r"""
Helper method for :meth:`__repr__`.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: morphism = S.subdivide_edges(2)
sage: morphism
Edge-Subdivision morphism:
From: Translation Surface in H_2(2) built from a regular octagon
To: Translation Surface in H_2(2, 0^4) built from a regular octagon with 8 marked vertices
"""
return "Edge-Subdivision"
[docs]
def __eq__(self, other):
r"""
Return whether this morphism is indistinguishable from ``other``.
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: S.subdivide_edges(2) == S.subdivide_edges(2)
True
"""
if not isinstance(other, SubdivideEdgesMorphism):
return False
return self.parent() == other.parent() and self._parts == other._parts
[docs]
def __hash__(self):
r"""
Return a hash value for this morphism that is compatible with :meth:`__eq__`
EXAMPLES::
sage: from flatsurf import translation_surfaces
sage: S = translation_surfaces.regular_octagon()
sage: hash(S.subdivide_edges(2)) == hash(S.subdivide_edges(2))
True
"""
return hash(self._parts)