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plot.py
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plot.py
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"""
Functions for plotting polyhedra
"""
########################################################################
# Copyright (C) 2008 Marshall Hampton <hamptonio@gmail.com>
# Copyright (C) 2011 Volker Braun <vbraun.name@gmail.com>
#
# Distributed under the terms of the GNU General Public License (GPL)
#
# http://www.gnu.org/licenses/
########################################################################
from __future__ import print_function, absolute_import
from sage.rings.all import RDF
from sage.structure.sage_object import SageObject
from sage.modules.free_module_element import vector
from sage.matrix.constructor import matrix, identity_matrix
from sage.misc.functional import norm
from sage.misc.latex import LatexExpr
from sage.symbolic.constants import pi
from sage.structure.sequence import Sequence
from sage.plot.all import Graphics, point2d, line2d, arrow, polygon2d
from sage.plot.plot3d.all import point3d, line3d, arrow3d, polygons3d
from sage.plot.plot3d.transform import rotate_arbitrary
from .base import is_Polyhedron
#############################################################
def render_2d(projection, *args, **kwds):
"""
Return 2d rendering of the projection of a polyhedron into
2-dimensional ambient space.
EXAMPLES::
sage: p1 = Polyhedron(vertices=[[1,1]], rays=[[1,1]])
sage: q1 = p1.projection()
sage: p2 = Polyhedron(vertices=[[1,0], [0,1], [0,0]])
sage: q2 = p2.projection()
sage: p3 = Polyhedron(vertices=[[1,2]])
sage: q3 = p3.projection()
sage: p4 = Polyhedron(vertices=[[2,0]], rays=[[1,-1]], lines=[[1,1]])
sage: q4 = p4.projection()
sage: q1.plot() + q2.plot() + q3.plot() + q4.plot()
Graphics object consisting of 17 graphics primitives
sage: from sage.geometry.polyhedron.plot import render_2d
sage: q = render_2d(p1.projection())
doctest:...: DeprecationWarning: use Projection.render_2d instead
See http://trac.sagemath.org/16625 for details.
sage: q._objects
[Point set defined by 1 point(s),
Arrow from (1.0,1.0) to (2.0,2.0),
Polygon defined by 3 points]
"""
from sage.misc.superseded import deprecation
deprecation(16625, 'use Projection.render_2d instead')
if is_Polyhedron(projection):
projection = Projection(projection)
return projection.render_2d(*args, **kwds)
def render_3d(projection, *args, **kwds):
"""
Return 3d rendering of a polyhedron projected into
3-dimensional ambient space.
.. NOTE::
This method, ``render_3d``, is used in the ``show()``
method of a polyhedron if it is in 3 dimensions.
EXAMPLES::
sage: p1 = Polyhedron(vertices=[[1,1,1]], rays=[[1,1,1]])
sage: p2 = Polyhedron(vertices=[[2,0,0], [0,2,0], [0,0,2]])
sage: p3 = Polyhedron(vertices=[[1,0,0], [0,1,0], [0,0,1]], rays=[[-1,-1,-1]])
sage: p1.projection().plot() + p2.projection().plot() + p3.projection().plot() # long time ~2sec
Graphics3d Object
It correctly handles various degenerate cases::
sage: Polyhedron(lines=[[1,0,0],[0,1,0],[0,0,1]]).plot() # whole space
Graphics3d Object
sage: Polyhedron(vertices=[[1,1,1]], rays=[[1,0,0]], lines=[[0,1,0],[0,0,1]]).plot() # half space
Graphics3d Object
sage: Polyhedron(vertices=[[1,1,1]], lines=[[0,1,0],[0,0,1]]).plot() # R^2 in R^3
Graphics3d Object
sage: Polyhedron(rays=[[0,1,0],[0,0,1]], lines=[[1,0,0]]).plot() # long time quadrant wedge in R^2
Graphics3d Object
sage: Polyhedron(rays=[[0,1,0]], lines=[[1,0,0]]).plot() # upper half plane in R^3
Graphics3d Object
sage: Polyhedron(lines=[[1,0,0]]).plot() # R^1 in R^2
Graphics3d Object
sage: Polyhedron(rays=[[0,1,0]]).plot() # Half-line in R^3
Graphics3d Object
sage: Polyhedron(vertices=[[1,1,1]]).plot() # point in R^3
Graphics3d Object
"""
from sage.misc.superseded import deprecation
deprecation(16625, 'use Projection.render_3d instead')
if is_Polyhedron(projection):
projection = Projection(projection)
return projection.render_3d(*args, **kwds)
def render_4d(polyhedron, point_opts={}, line_opts={}, polygon_opts={}, projection_direction=None):
"""
Return a 3d rendering of the Schlegel projection of a 4d
polyhedron projected into 3-dimensional space.
.. NOTE::
The ``show()`` method of ``Polyhedron()`` uses this to draw itself
if the ambient dimension is 4.
INPUT:
- ``polyhedron`` -- A
:mod:`~sage.geometry.polyhedron.constructor.Polyhedron` object.
- ``point_opts``, ``line_opts``, ``polygon_opts`` -- dictionaries
of plot keywords or ``False`` to disable.
- ``projection_direction`` -- list/tuple/iterable of coordinates
or ``None`` (default). Sets the projection direction of the
Schlegel projection. If it is not given, the center of a facet
is used.
EXAMPLES::
sage: poly = polytopes.twenty_four_cell()
sage: poly
A 4-dimensional polyhedron in QQ^4 defined as the convex hull of 24 vertices
sage: poly.plot() # long time
Graphics3d Object
sage: poly.plot(projection_direction=[2,5,11,17]) # long time ~2sec
Graphics3d Object
sage: type( poly.plot() )
<class 'sage.plot.plot3d.base.Graphics3dGroup'>
TESTS::
sage: from sage.geometry.polyhedron.plot import render_4d
sage: p = polytopes.hypercube(4)
sage: q = render_4d(p)
doctest:...: DeprecationWarning: use Polyhedron.schlegel_projection instead
See http://trac.sagemath.org/16625 for details.
doctest:...: DeprecationWarning: use Projection.render_3d instead
See http://trac.sagemath.org/16625 for details.
sage: tach_str = q.tachyon()
sage: tach_str.count('FCylinder')
32
"""
from sage.misc.superseded import deprecation
deprecation(16625, 'use Polyhedron.schlegel_projection instead')
if projection_direction is None:
for ineq in polyhedron.inequality_generator():
center = [v() for v in ineq.incident() if v.is_vertex()]
center = sum(center) / len(center)
if not center.is_zero():
projection_direction = center
break
projection_3d = Projection(polyhedron).schlegel(projection_direction)
return render_3d(projection_3d, point_opts, line_opts, polygon_opts)
#############################################################
def cyclic_sort_vertices_2d(Vlist):
"""
Return the vertices/rays in cyclic order if possible.
.. NOTE::
This works if and only if each vertex/ray is adjacent to exactly
two others. For example, any 2-dimensional polyhedron satisfies
this.
See
:meth:`~sage.geometry.polyhedron.base.Polyhedron_base.vertex_adjacency_matrix`
for a discussion of "adjacent".
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import cyclic_sort_vertices_2d
sage: square = Polyhedron([[1,0],[-1,0],[0,1],[0,-1]])
sage: vertices = [v for v in square.vertex_generator()]
sage: vertices
[A vertex at (-1, 0),
A vertex at (0, -1),
A vertex at (0, 1),
A vertex at (1, 0)]
sage: cyclic_sort_vertices_2d(vertices)
[A vertex at (1, 0),
A vertex at (0, -1),
A vertex at (-1, 0),
A vertex at (0, 1)]
Rays are allowed, too::
sage: P = Polyhedron(vertices=[(0, 1), (1, 0), (2, 0), (3, 0), (4, 1)], rays=[(0,1)])
sage: P.adjacency_matrix()
[0 1 0 1 0]
[1 0 1 0 0]
[0 1 0 0 1]
[1 0 0 0 1]
[0 0 1 1 0]
sage: cyclic_sort_vertices_2d(P.Vrepresentation())
[A vertex at (3, 0),
A vertex at (1, 0),
A vertex at (0, 1),
A ray in the direction (0, 1),
A vertex at (4, 1)]
sage: P = Polyhedron(vertices=[(0, 1), (1, 0), (2, 0), (3, 0), (4, 1)], rays=[(0,1), (1,1)])
sage: P.adjacency_matrix()
[0 1 0 0 0]
[1 0 1 0 0]
[0 1 0 0 1]
[0 0 0 0 1]
[0 0 1 1 0]
sage: cyclic_sort_vertices_2d(P.Vrepresentation())
[A ray in the direction (1, 1),
A vertex at (3, 0),
A vertex at (1, 0),
A vertex at (0, 1),
A ray in the direction (0, 1)]
sage: P = Polyhedron(vertices=[(1,2)], rays=[(0,1)], lines=[(1,0)])
sage: P.adjacency_matrix()
[0 0 1]
[0 0 0]
[1 0 0]
sage: cyclic_sort_vertices_2d(P.Vrepresentation())
[A vertex at (0, 2),
A line in the direction (1, 0),
A ray in the direction (0, 1)]
"""
if not Vlist:
return Vlist
Vlist = list(Vlist)
result = []
adjacency_matrix = Vlist[0].polyhedron().vertex_adjacency_matrix()
# Any object in Vlist has 0,1, or 2 adjacencies. Break into connected chains:
chain = [Vlist.pop()]
while Vlist:
first_index = chain[0].index()
last_index = chain[-1].index()
for v in Vlist:
v_index = v.index()
if adjacency_matrix[last_index, v_index] == 1:
chain = chain + [v]
Vlist.remove(v)
break
if adjacency_matrix[first_index, v.index()] == 1:
chain = [v] + chain
Vlist.remove(v)
break
else:
result += chain
chain = [ Vlist.pop() ]
result += chain
return result
#########################################################################
def projection_func_identity(x):
"""
The identity projection.
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import projection_func_identity
sage: projection_func_identity((1,2,3))
[1, 2, 3]
"""
return list(x)
class ProjectionFuncStereographic():
"""
The stereographic (or perspective) projection.
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import ProjectionFuncStereographic
sage: cube = polytopes.hypercube(3).vertices()
sage: proj = ProjectionFuncStereographic([1.2, 3.4, 5.6])
sage: ppoints = [proj(vector(x)) for x in cube]
sage: ppoints[0]
(-0.0486511..., 0.0859565...)
"""
def __init__(self, projection_point):
"""
Create a stereographic projection function.
INPUT:
- ``projection_point`` -- a list of coordinates in the
appropriate dimension, which is the point projected from.
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import ProjectionFuncStereographic
sage: proj = ProjectionFuncStereographic([1.0,1.0])
sage: proj.__init__([1.0,1.0])
sage: proj.house
[-0.7071067811... 0.7071067811...]
[ 0.7071067811... 0.7071067811...]
sage: TestSuite(proj).run(skip='_test_pickling')
"""
self.projection_point = vector(projection_point)
self.dim = self.projection_point.degree()
pproj = vector(RDF, self.projection_point)
self.psize = norm(pproj)
if (self.psize).is_zero():
raise ValueError("projection direction must be a non-zero vector.")
v = vector(RDF, [0.0]*(self.dim-1) + [self.psize]) - pproj
polediff = matrix(RDF, v).transpose()
denom = RDF((polediff.transpose()*polediff)[0][0])
if denom.is_zero():
self.house = identity_matrix(RDF, self.dim)
else:
self.house = identity_matrix(RDF, self.dim) \
- 2*polediff*polediff.transpose()/denom # Householder reflector
def __call__(self, x):
"""
Action of the stereographic projection.
INPUT:
- ``x`` -- a vector or anything convertible to a vector.
OUTPUT:
First reflects ``x`` with a Householder reflection which takes
the projection point to ``(0,...,0,self.psize)`` where
``psize`` is the length of the projection point, and then
dilates by ``1/(zdiff)`` where ``zdiff`` is the difference
between the last coordinate of ``x`` and ``psize``.
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import ProjectionFuncStereographic
sage: proj = ProjectionFuncStereographic([1.0,1.0])
sage: proj.__call__(vector([1,2]))
(-1.0000000000000002)
sage: proj = ProjectionFuncStereographic([2.0,1.0])
sage: proj.__call__(vector([1,2])) # abs tol 1e-14
(2.9999999999999996)
sage: proj = ProjectionFuncStereographic([0,0,2])
sage: proj.__call__(vector([0,0,1]))
(0.0, 0.0)
sage: proj.__call__(vector([1,0,0]))
(0.5, 0.0)
"""
img = self.house * x
denom = self.psize-img[self.dim-1]
if denom.is_zero():
raise ValueError('Point cannot coincide with ' \
'coordinate singularity at ' + repr(x))
return vector(RDF, [img[i]/denom for i in range(self.dim-1)])
class ProjectionFuncSchlegel():
"""
The Schlegel projection from the given input point.
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import ProjectionFuncSchlegel
sage: proj = ProjectionFuncSchlegel([2,2,2])
sage: proj(vector([1.1,1.1,1.11]))[0]
0.0302...
"""
def __init__(self, projection_direction, height=1.1, center=0):
"""
Initializes the projection.
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import ProjectionFuncSchlegel
sage: proj = ProjectionFuncSchlegel([2,2,2])
sage: proj.__init__([2,2,2])
sage: proj(vector([1.1,1.1,1.11]))[0]
0.0302...
sage: TestSuite(proj).run(skip='_test_pickling')
"""
self.center = center
self.projection_dir = vector(RDF, projection_direction)
if norm(self.projection_dir).is_zero():
raise ValueError("projection direction must be a non-zero vector.")
self.dim = self.projection_dir.degree()
spcenter = height * self.projection_dir/norm(self.projection_dir)
self.height = height
v = vector(RDF, [0.0]*(self.dim-1) + [self.height]) - spcenter
polediff = matrix(RDF, v).transpose()
denom = (polediff.transpose()*polediff)[0][0]
if denom.is_zero():
self.house = identity_matrix(RDF, self.dim)
else:
self.house = identity_matrix(RDF, self.dim) \
- 2*polediff*polediff.transpose()/denom # Householder reflector
def __call__(self, x):
"""
Apply the projection to a vector.
- ``x`` -- a vector or anything convertible to a vector.
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import ProjectionFuncSchlegel
sage: proj = ProjectionFuncSchlegel([2,2,2])
sage: proj.__call__([1,2,3])
(0.56162854..., 2.09602626...)
"""
v = vector(RDF, x) - self.center
if v.is_zero():
raise ValueError("The origin must not be a vertex.")
v = v/norm(v) # normalize vertices to unit sphere
v = self.house*v # reflect so self.projection_dir is at "north pole"
denom = self.height-v[self.dim-1]
if denom.is_zero():
raise ValueError('Point cannot coincide with ' \
'coordinate singularity at ' + repr(x))
return vector(RDF, [ v[i]/denom for i in range(self.dim-1) ])
#########################################################################
class Projection(SageObject):
"""
The projection of a :class:`Polyhedron`.
This class keeps track of the necessary data to plot the input
polyhedron.
"""
def __init__(self, polyhedron, proj=projection_func_identity):
"""
Initialize the projection of a Polyhedron() object.
INPUT:
- ``polyhedron`` -- a ``Polyhedron()`` object
- ``proj`` -- a projection function for the points
.. NOTE::
Once initialized, the polyhedral data is fixed. However, the
projection can be changed later on.
EXAMPLES::
sage: p = polytopes.icosahedron(exact=False)
sage: from sage.geometry.polyhedron.plot import Projection
sage: Projection(p)
The projection of a polyhedron into 3 dimensions
sage: def pr_12(x): return [x[1],x[2]]
sage: Projection(p, pr_12)
The projection of a polyhedron into 2 dimensions
sage: Projection(p, lambda x: [x[1],x[2]] ) # another way of doing the same projection
The projection of a polyhedron into 2 dimensions
sage: _.plot() # plot of the projected icosahedron in 2d
Graphics object consisting of 51 graphics primitives
sage: proj = Projection(p)
sage: proj.stereographic([1,2,3])
The projection of a polyhedron into 2 dimensions
sage: proj.plot()
Graphics object consisting of 51 graphics primitives
sage: TestSuite(proj).run(skip='_test_pickling')
"""
self.parent_polyhedron = polyhedron
self.coords = Sequence([])
self.points = Sequence([])
self.lines = Sequence([])
self.arrows = Sequence([])
self.polygons = Sequence([])
self.polyhedron_ambient_dim = polyhedron.ambient_dim()
self.polyhedron_dim = polyhedron.dim()
if polyhedron.ambient_dim() == 2:
self._init_from_2d(polyhedron)
elif polyhedron.ambient_dim() == 3:
self._init_from_3d(polyhedron)
else:
self._init_points(polyhedron)
self._init_lines_arrows(polyhedron)
self.coords.set_immutable()
self.points.set_immutable()
self.lines.set_immutable()
self.arrows.set_immutable()
self.polygons.set_immutable()
self(proj)
def _repr_(self):
"""
Return a string describing the projection.
EXAMPLES::
sage: p = polytopes.hypercube(3)
sage: from sage.geometry.polyhedron.plot import Projection
sage: proj = Projection(p)
sage: print(proj._repr_())
The projection of a polyhedron into 3 dimensions
"""
s = 'The projection of a polyhedron into ' + \
repr(self.dimension) + ' dimensions'
return s
def __call__(self, proj=projection_func_identity):
"""
Apply a projection.
EXAMPLES::
sage: p = polytopes.icosahedron(exact=False)
sage: from sage.geometry.polyhedron.plot import Projection
sage: pproj = Projection(p)
sage: from sage.geometry.polyhedron.plot import ProjectionFuncStereographic
sage: pproj_stereo = pproj.__call__(proj = ProjectionFuncStereographic([1,2,3]))
sage: pproj_stereo.polygons[0]
[10, 1, 4]
"""
self.transformed_coords = \
Sequence([proj(p) for p in self.coords])
self._init_dimension()
return self
def identity(self):
"""
Return the identity projection of the polyhedron.
EXAMPLES::
sage: p = polytopes.icosahedron(exact=False)
sage: from sage.geometry.polyhedron.plot import Projection
sage: pproj = Projection(p)
sage: ppid = pproj.identity()
sage: ppid.dimension
3
"""
return self(projection_func_identity)
def stereographic(self, projection_point=None):
r"""
Return the stereographic projection.
INPUT:
- ``projection_point`` - The projection point. This must be
distinct from the polyhedron's vertices. Default is `(1,0,\dots,0)`
EXAMPLES::
sage: from sage.geometry.polyhedron.plot import Projection
sage: proj = Projection(polytopes.buckyball()) #long time
sage: proj #long time
The projection of a polyhedron into 3 dimensions
sage: proj.stereographic([5,2,3]).plot() #long time
Graphics object consisting of 123 graphics primitives
sage: Projection( polytopes.twenty_four_cell() ).stereographic([2,0,0,0])
The projection of a polyhedron into 3 dimensions
"""
if projection_point is None:
projection_point = [1] + [0]*(self.polyhedron_ambient_dim-1)
return self(ProjectionFuncStereographic(projection_point))
def schlegel(self, projection_direction=None, height=1.1):
"""
Return the Schlegel projection.
* The polyhedron is translated such that its
:meth:`~sage.geometry.polyhedron.base.Polyhedron_base.center`
is at the origin.
* The vertices are then normalized to the unit sphere
* The normalized points are stereographically projected from a
point slightly outside of the sphere.
INPUT:
- ``projection_direction`` -- coordinate list/tuple/iterable
or ``None`` (default). The direction of the Schlegel
projection. For a full-dimensional polyhedron, the default
is the first facet normal; Otherwise, the vector consisting
of the first n primes is chosen.
- ``height`` -- float (default: `1.1`). How far outside of the
unit sphere the focal point is.
EXAMPLES::
sage: cube4 = polytopes.hypercube(4)
sage: from sage.geometry.polyhedron.plot import Projection
sage: Projection(cube4).schlegel([1,0,0,0])
The projection of a polyhedron into 3 dimensions
sage: _.plot()
Graphics3d Object
TESTS::
sage: Projection(cube4).schlegel()
The projection of a polyhedron into 3 dimensions
"""
center = self.parent_polyhedron.center()
if projection_direction is None:
if self.parent_polyhedron.is_full_dimensional():
projection_direction = next(self.parent_polyhedron.inequality_generator()).A()
else:
from sage.arith.all import primes_first_n
projection_direction = primes_first_n(self.polyhedron_ambient_dim)
return self(ProjectionFuncSchlegel(
projection_direction, height=height, center=center))
def coord_index_of(self, v):
"""
Convert a coordinate vector to its internal index.
EXAMPLES::
sage: p = polytopes.hypercube(3)
sage: proj = p.projection()
sage: proj.coord_index_of(vector((1,1,1)))
7
"""
try:
return self.coords.index(v)
except ValueError:
self.coords.append(v)
return len(self.coords)-1
def coord_indices_of(self, v_list):
"""
Convert list of coordinate vectors to the corresponding list
of internal indices.
EXAMPLES::
sage: p = polytopes.hypercube(3)
sage: proj = p.projection()
sage: proj.coord_indices_of([vector((1,1,1)),vector((1,-1,1))])
[7, 5]
"""
return [self.coord_index_of(v) for v in v_list]
def coordinates_of(self, coord_index_list):
"""
Given a list of indices, return the projected coordinates.
EXAMPLES::
sage: p = polytopes.simplex(4, project=True).projection()
sage: p.coordinates_of([1])
[[-0.7071067812, 0.4082482905, 0.2886751346, 0.2236067977]]
"""
return [self.transformed_coords[i] for i in coord_index_list]
def _init_dimension(self):
"""
Internal function: Initialize from polyhedron with
projected coordinates. Must always be called after
a coordinate projection.
TESTS::
sage: from sage.geometry.polyhedron.plot import Projection, render_2d
sage: p = polytopes.simplex(2, project=True).projection()
sage: test = p._init_dimension()
sage: p.plot.__doc__ == p.render_2d.__doc__
True
"""
if self.transformed_coords:
self.dimension = len(self.transformed_coords[0])
else:
self.dimension = 0
if self.dimension == 0:
self.plot = self.render_0d
elif self.dimension == 1:
self.plot = self.render_1d
elif self.dimension == 2:
self.plot = self.render_2d
elif self.dimension == 3:
self.plot = self.render_3d
else:
try:
del self.plot
except AttributeError:
pass
def show(self, *args, **kwds):
"""
Deprecated method to show the projection as a graphics
object. Use ``Projection.plot()`` instead.
EXAMPLES::
sage: P8 = polytopes.hypercube(4)
sage: P8.schlegel_projection([2,5,11,17]).show()
doctest:...: DeprecationWarning: use Projection.plot instead
See http://trac.sagemath.org/16625 for details.
Graphics3d Object
"""
from sage.misc.superseded import deprecation
deprecation(16625, 'use Projection.plot instead')
return self.plot(*args, **kwds)
def _init_from_2d(self, polyhedron):
"""
Internal function: Initialize from polyhedron in
2-dimensional space. The polyhedron could be lower
dimensional.
TESTS::
sage: p = Polyhedron(vertices = [[0,0],[0,1],[1,0],[1,1]])
sage: proj = p.projection()
sage: [proj.coordinates_of([i]) for i in proj.points]
[[[0, 0]], [[0, 1]], [[1, 0]], [[1, 1]]]
sage: proj._init_from_2d
<bound method Projection._init_from_2d of The projection
of a polyhedron into 2 dimensions>
"""
assert polyhedron.ambient_dim() == 2, "Requires polyhedron in 2d"
self.dimension = 2
self._init_points(polyhedron)
self._init_lines_arrows(polyhedron)
self._init_area_2d(polyhedron)
def _init_from_3d(self, polyhedron):
"""
Internal function: Initialize from polyhedron in
3-dimensional space. The polyhedron could be
lower dimensional.
TESTS::
sage: p = Polyhedron(vertices = [[0,0,1],[0,1,2],[1,0,3],[1,1,5]])
sage: proj = p.projection()
sage: [proj.coordinates_of([i]) for i in proj.points]
[[[0, 0, 1]], [[0, 1, 2]], [[1, 0, 3]], [[1, 1, 5]]]
sage: proj._init_from_3d
<bound method Projection._init_from_3d of The projection
of a polyhedron into 3 dimensions>
"""
assert polyhedron.ambient_dim() == 3, "Requires polyhedron in 3d"
self.dimension = 3
self._init_points(polyhedron)
self._init_lines_arrows(polyhedron)
self._init_solid_3d(polyhedron)
def _init_points(self, polyhedron):
"""
Internal function: Initialize points (works in arbitrary
dimensions).
TESTS::
sage: p = polytopes.hypercube(2)
sage: pp = p.projection()
sage: del pp.points
sage: pp.points = Sequence([])
sage: pp._init_points(p)
sage: pp.points
[0, 1, 2, 3]
"""
for v in polyhedron.vertex_generator():
self.points.append( self.coord_index_of(v.vector()) )
def _init_lines_arrows(self, polyhedron):
"""
Internal function: Initialize compact and non-compact edges
(works in arbitrary dimensions).
TESTS::
sage: p = Polyhedron(ieqs = [[1, 0, 0, 1],[1,1,0,0]])
sage: pp = p.projection()
sage: pp.arrows
[[0, 1], [0, 2]]
sage: del pp.arrows
sage: pp.arrows = Sequence([])
sage: pp._init_lines_arrows(p)
sage: pp.arrows
[[0, 1], [0, 2]]
"""
obj = polyhedron.Vrepresentation()
for i in range(len(obj)):
if not obj[i].is_vertex(): continue
for j in range(len(obj)):
if polyhedron.vertex_adjacency_matrix()[i,j] == 0: continue
if i < j and obj[j].is_vertex():
l = [obj[i].vector(), obj[j].vector()]
self.lines.append( [ self.coord_index_of(l[0]),
self.coord_index_of(l[1]) ] )
if obj[j].is_ray():
l = [obj[i].vector(), obj[i].vector() + obj[j].vector()]
self.arrows.append( [ self.coord_index_of(l[0]),
self.coord_index_of(l[1]) ] )
if obj[j].is_line():
l1 = [obj[i].vector(), obj[i].vector() + obj[j].vector()]
l2 = [obj[i].vector(), obj[i].vector() - obj[j].vector()]
self.arrows.append( [ self.coord_index_of(l1[0]),
self.coord_index_of(l1[1]) ] )
self.arrows.append( [ self.coord_index_of(l2[0]),
self.coord_index_of(l2[1]) ] )
def _init_area_2d(self, polyhedron):
"""
Internal function: Initialize polygon area for 2d polyhedron.
TESTS::
sage: p = polytopes.cyclic_polytope(2,4)
sage: proj = p.projection()
sage: proj.polygons = Sequence([])
sage: proj._init_area_2d(p)
sage: proj.polygons
[[3, 0, 1, 2]]
"""
assert polyhedron.ambient_dim() == 2, "Requires polyhedron in 2d"
vertices = [v for v in polyhedron.Vrep_generator()]
vertices = cyclic_sort_vertices_2d(vertices)
coords = []
def adjacent_vertices(i):
n = len(vertices)
if vertices[(i-1) % n].is_vertex(): yield vertices[(i-1) % n]
if vertices[(i+1) % n].is_vertex(): yield vertices[(i+1) % n]
for i in range(len(vertices)):
v = vertices[i]
if v.is_vertex():
coords.append(v())
if v.is_ray():
for a in adjacent_vertices(i):
coords.append(a() + v())
if polyhedron.n_lines() == 0:
self.polygons.append( self.coord_indices_of(coords) )
return
polygons = []
if polyhedron.n_lines() == 1:
aline = next(polyhedron.line_generator())
for shift in [aline(), -aline()]:
for i in range(len(coords)):
polygons.append( [ coords[i-1],coords[i],
coords[i]+shift, coords[i-1]+shift ] )
if polyhedron.n_lines() == 2:
[line1, line2] = [l for l in polyhedron.lines()]
assert len(coords) == 1, "Can have only a single vertex!"
v = coords[0]
l1 = line1()
l2 = line2()
polygons = [ [v-l1-l2, v+l1-l2, v+l1+l2, v-l1+l2] ]
polygons = [ self.coord_indices_of(p) for p in polygons ]
self.polygons.extend(polygons)
def _init_solid_3d(self, polyhedron):
"""
Internal function: Initialize facet polygons for 3d polyhedron.
TESTS::
sage: p = polytopes.cyclic_polytope(3,4)
sage: proj = p.projection()
sage: proj.polygons = Sequence([])
sage: proj._init_solid_3d(p)
sage: proj.polygons
[[1, 0, 2], [3, 0, 1], [2, 0, 3], [3, 1, 2]]
"""
assert polyhedron.ambient_dim() == 3, "Requires polyhedron in 3d"
if polyhedron.dim() <= 1: # empty or 0d or 1d polyhedron => no polygon
return None
def defining_equation(): # corresponding to a polygon
if polyhedron.dim() < 3:
yield next(polyhedron.equation_generator())
else:
for ineq in polyhedron.inequality_generator():
yield ineq
faces = []
face_inequalities = []
for facet_equation in defining_equation():
vertices = [v for v in facet_equation.incident()]
face_inequalities.append(facet_equation)
vertices = cyclic_sort_vertices_2d(vertices)
if len(vertices) >= 3:
v0, v1, v2 = [vector(v) for v in vertices[:3]]
normal = (v2 - v0).cross_product(v1 - v0)
if normal.dot_product(facet_equation.A()) < 0:
vertices.reverse()
coords = []
def adjacent_vertices(i):
n = len(vertices)
if vertices[(i-1) % n].is_vertex(): yield vertices[(i-1) % n]
if vertices[(i+1) % n].is_vertex(): yield vertices[(i+1) % n]
for i in range(len(vertices)):
v = vertices[i]
if v.is_vertex():
coords.append(v())
if v.is_ray():
for a in adjacent_vertices(i):
coords.append(a() + v())
faces.append(coords)
self.face_inequalities = face_inequalities
if polyhedron.n_lines() == 0:
assert len(faces) > 0, "no vertices?"
self.polygons.extend( [self.coord_indices_of(f) for f in faces] )
return
# now some special cases if there are lines (dim < ambient_dim)
polygons = []
if polyhedron.n_lines() == 1:
assert len(faces) > 0, "no vertices?"
aline = next(polyhedron.line_generator())
for shift in [aline(), -aline()]:
for coords in faces:
assert len(coords) == 2, "There must be two points."
polygons.append( [ coords[0],coords[1],
coords[1]+shift, coords[0]+shift ] )
if polyhedron.n_lines() == 2:
[line1, line2] = [l for l in polyhedron.line_generator()]
l1 = line1()
l2 = line2()
for v in polyhedron.vertex_generator():
polygons.append( [v()-l1-l2, v()+l1-l2, v()+l1+l2, v()-l1+l2] )
self.polygons.extend( [self.coord_indices_of(p) for p in polygons] )
def render_points_1d(self, **kwds):
"""
Return the points of a polyhedron in 1d.
INPUT:
- ``**kwds`` -- options passed through to
:func:`~sage.plot.point.point2d`.
OUTPUT:
A 2-d graphics object.
EXAMPLES::
sage: cube1 = polytopes.hypercube(1)
sage: proj = cube1.projection()
sage: points = proj.render_points_1d()
sage: points._objects
[Point set defined by 2 point(s)]
"""
return point2d([c + [0] for c in self.coordinates_of(self.points)], **kwds)
def render_line_1d(self, **kwds):
"""
Return the line of a polyhedron in 1d.
INPUT:
- ``**kwds`` -- options passed through to
:func:`~sage.plot.line.line2d`.
OUTPUT: