Hyperbolic Points

This module implements points in hyperbolic space of arbitrary dimension. It also contains the implementations for specific models of hyperbolic geometry.

This module also implements ideal points in hyperbolic space of arbitrary dimension. It also contains the implementations for specific models of hyperbolic geometry.

Note that not all models of hyperbolic space are bounded, meaning that the ideal boundary is not the topological boundary of the set underlying tho model. For example, the unit disk model is bounded with boundary given by the unit sphere. The hyperboloid model is not bounded.

AUTHORS:

• Greg Laun (2013): initial version

EXAMPLES:

We can construct points in the upper half plane model, abbreviated UHP for convenience:

sage: UHP = HyperbolicPlane().UHP()
sage: UHP.get_point(2 + I)
Point in UHP I + 2
sage: g = UHP.get_point(3 + I)
sage: g.dist(UHP.get_point(I))
arccosh(11/2)

We can also construct boundary points in the upper half plane model:

sage: UHP.get_point(3)
Boundary point in UHP 3

Some more examples:

sage: HyperbolicPlane().UHP().get_point(0)
Boundary point in UHP 0

sage: HyperbolicPlane().PD().get_point(I/2)
Point in PD 1/2*I

sage: HyperbolicPlane().KM().get_point((0,1))
Boundary point in KM (0, 1)

sage: HyperbolicPlane().HM().get_point((0,0,1))
Point in HM (0, 0, 1)

class sage.geometry.hyperbolic_space.hyperbolic_point.HyperbolicPoint(model, coordinates, is_boundary, check=True, **graphics_options)

Bases: sage.structure.element.Element

Abstract base class for hyperbolic points. This class should never be instantiated.

INPUT:

• model – the model of the hyperbolic space

• coordinates – the coordinates of a hyperbolic point in the appropriate model

• is_boundary – whether the point is a boundary point

• check – (default: True) if True, then check to make sure the coordinates give a valid point in the model

EXAMPLES:

Comparison between different models is performed via coercion:

sage: UHP = HyperbolicPlane().UHP()
sage: p = UHP.get_point(.2 + .3*I); p
Point in UHP 0.200000000000000 + 0.300000000000000*I

sage: PD = HyperbolicPlane().PD()
sage: q = PD.get_point(0.2 + 0.3*I); q
Point in PD 0.200000000000000 + 0.300000000000000*I

sage: p == q
False
sage: PD(p)
Point in PD 0.231213872832370 - 0.502890173410405*I

sage: bool(p.coordinates() == q.coordinates())
True

Similarly for boundary points:

sage: p = UHP.get_point(-1); p
Boundary point in UHP -1

sage: q = PD.get_point(-1); q
Boundary point in PD -1

sage: p == q
True
sage: PD(p)
Boundary point in PD -1

It is an error to specify a point that does not lie in the appropriate model:

sage: HyperbolicPlane().UHP().get_point(0.2 - 0.3*I)
Traceback (most recent call last):
...
ValueError: 0.200000000000000 - 0.300000000000000*I is not a valid point in the UHP model

sage: HyperbolicPlane().PD().get_point(1.2)
Traceback (most recent call last):
...
ValueError: 1.20000000000000 is not a valid point in the PD model

sage: HyperbolicPlane().KM().get_point((1,1))
Traceback (most recent call last):
...
ValueError: (1, 1) is not a valid point in the KM model

sage: HyperbolicPlane().HM().get_point((1, 1, 1))
Traceback (most recent call last):
...
ValueError: (1, 1, 1) is not a valid point in the HM model

It is an error to specify an interior point of hyperbolic space as a boundary point:

sage: HyperbolicPlane().UHP().get_point(0.2 + 0.3*I, is_boundary=True)
Traceback (most recent call last):
...
ValueError: 0.200000000000000 + 0.300000000000000*I is not a valid boundary point in the UHP model

coordinates()

Return the coordinates of the point.

EXAMPLES:

sage: HyperbolicPlane().UHP().get_point(2 + I).coordinates()
I + 2

sage: HyperbolicPlane().PD().get_point(1/2 + 1/2*I).coordinates()
1/2*I + 1/2

sage: HyperbolicPlane().KM().get_point((1/3, 1/4)).coordinates()
(1/3, 1/4)

sage: HyperbolicPlane().HM().get_point((0,0,1)).coordinates()
(0, 0, 1)

graphics_options()

Return the graphics options of the current point.

EXAMPLES:

sage: p = HyperbolicPlane().UHP().get_point(2 + I, color="red")
sage: p.graphics_options()
{'color': 'red'}

is_boundary()

Return True if self is a boundary point.

EXAMPLES:

sage: PD = HyperbolicPlane().PD()
sage: p = PD.get_point(0.5+.2*I)
sage: p.is_boundary()
False
sage: p = PD.get_point(I)
sage: p.is_boundary()
True

model()

Return the model to which the HyperbolicPoint belongs.

EXAMPLES:

sage: HyperbolicPlane().UHP().get_point(I).model()
Hyperbolic plane in the Upper Half Plane Model

sage: HyperbolicPlane().PD().get_point(0).model()
Hyperbolic plane in the Poincare Disk Model

sage: HyperbolicPlane().KM().get_point((0,0)).model()
Hyperbolic plane in the Klein Disk Model

sage: HyperbolicPlane().HM().get_point((0,0,1)).model()
Hyperbolic plane in the Hyperboloid Model

show(boundary=True, **options)

Plot self.

EXAMPLES:

sage: HyperbolicPlane().PD().get_point(0).show()
Graphics object consisting of 2 graphics primitives
sage: HyperbolicPlane().KM().get_point((0,0)).show()
Graphics object consisting of 2 graphics primitives
sage: HyperbolicPlane().HM().get_point((0,0,1)).show()
Graphics3d Object

symmetry_involution()

Return the involutory isometry fixing the given point.

EXAMPLES:

sage: z = HyperbolicPlane().UHP().get_point(3 + 2*I)
sage: z.symmetry_involution()
Isometry in UHP
[  3/2 -13/2]
[  1/2  -3/2]

sage: HyperbolicPlane().UHP().get_point(I).symmetry_involution()
Isometry in UHP
[ 0 -1]
[ 1  0]

sage: HyperbolicPlane().PD().get_point(0).symmetry_involution()
Isometry in PD
[-I  0]
[ 0  I]

sage: HyperbolicPlane().KM().get_point((0, 0)).symmetry_involution()
Isometry in KM
[-1  0  0]
[ 0 -1  0]
[ 0  0  1]

sage: HyperbolicPlane().HM().get_point((0,0,1)).symmetry_involution()
Isometry in HM
[-1  0  0]
[ 0 -1  0]
[ 0  0  1]

sage: p = HyperbolicPlane().UHP().random_element()
sage: A = p.symmetry_involution()
sage: p.dist(A*p)  # abs tol 1e-10
0

sage: A.preserves_orientation()
True

sage: A*A == HyperbolicPlane().UHP().get_isometry(identity_matrix(2))
True

to_model(model)

Convert self to the model.

INPUT:

• other – (a string representing) the image model

EXAMPLES:

sage: UHP = HyperbolicPlane().UHP()
sage: PD = HyperbolicPlane().PD()
sage: PD.get_point(1/2+I/2).to_model(UHP)
Point in UHP I + 2
sage: PD.get_point(1/2+I/2).to_model('UHP')
Point in UHP I + 2

update_graphics(update=False, **options)

Update the graphics options of a HyperbolicPoint. If update is True, update rather than overwrite.

EXAMPLES:

sage: p = HyperbolicPlane().UHP().get_point(I); p.graphics_options()
{}

sage: p.update_graphics(color = "red"); p.graphics_options()
{'color': 'red'}

sage: p.update_graphics(color = "blue"); p.graphics_options()
{'color': 'blue'}

sage: p.update_graphics(True, size = 20); p.graphics_options()
{'color': 'blue', 'size': 20}

class sage.geometry.hyperbolic_space.hyperbolic_point.HyperbolicPointUHP(model, coordinates, is_boundary, check=True, **graphics_options)

Bases: sage.geometry.hyperbolic_space.hyperbolic_point.HyperbolicPoint

A point in the UHP model.

INPUT:

• the coordinates of a point in the unit disk in the complex plane \(\CC\)

EXAMPLES:

sage: HyperbolicPlane().UHP().get_point(2*I)
Point in UHP 2*I

sage: HyperbolicPlane().UHP().get_point(1)
Boundary point in UHP 1

show(boundary=True, **options)

Plot self.

EXAMPLES:

sage: HyperbolicPlane().UHP().get_point(I).show()
Graphics object consisting of 2 graphics primitives
sage: HyperbolicPlane().UHP().get_point(0).show()
Graphics object consisting of 2 graphics primitives
sage: HyperbolicPlane().UHP().get_point(infinity).show()
Traceback (most recent call last):
...
NotImplementedError: can...t draw the point infinity

symmetry_involution()

Return the involutory isometry fixing the given point.

EXAMPLES:

sage: HyperbolicPlane().UHP().get_point(3 + 2*I).symmetry_involution()
Isometry in UHP
[  3/2 -13/2]
[  1/2  -3/2]