Cannot plot Cone that is a halfplane in 2d

[yuan-zhou]

sage: halfplane = Cone([(1,0), (0,1), (-1,0)])
sage: halfplane.plot() 

raises UnboundLocalError: local variable 'r1' referenced before assignment.

CC: @novoselt @jplab @mkoeppe @orlitzky

Component: geometry

Keywords: Cone, plot, IMA-PolyGeom

Branch/Commit: u/yzh/cannot_plot_cone_that_is_a_halfplane_in_2d @ 57f5898

Issue created by migration from https://trac.sagemath.org/ticket/25114

[yuan-zhou]

Branch: u/yzh/cannot_plot_cone_that_is_a_halfplane_in_2d

[yuan-zhou]

New commits:

959187f

represent the rays of wall by a matrix. add doctest

[yuan-zhou]

Commit: 959187f

[yuan-zhou]

Changed keywords from Cone, plot to Cone, plot, IMA-PolyGeom

[novoselt]

comment:3

While this may fix the plotting issue, it hides the real problem:

sage: N = ToricLattice(2); N
2-d lattice N
sage: NQ = N.base_extend(QQ); NQ
Vector space of dimension 2 over Rational Field
sage: r = N.gen(0); r
N(1, 0)
sage: S = N.submodule([r]); S
Sublattice <N(1, 0)>
sage: SQ = S.base_extend(QQ); SQ
 
Vector space of degree 2 and dimension 1 over Rational Field
Basis matrix:
[1 0]
sage: r in N, r in NQ
(True, True)
sage: r in S, r in SQ
(True, False)

Why is there this difference in behaviour of vector spaces and subspaces? The original code likely worked for halfplanes when it was written and there is no reason for it to stop.

[jplab]

comment:4

Replying to @novoselt:

While this may fix the plotting issue, it hides the real problem:

sage: N = ToricLattice(2); N
2-d lattice N
sage: NQ = N.base_extend(QQ); NQ
Vector space of dimension 2 over Rational Field
sage: r = N.gen(0); r
N(1, 0)
sage: S = N.submodule([r]); S
Sublattice <N(1, 0)>
sage: SQ = S.base_extend(QQ); SQ
 
Vector space of degree 2 and dimension 1 over Rational Field
Basis matrix:
[1 0]
sage: r in N, r in NQ
(True, True)
sage: r in S, r in SQ
(True, False)

Why is there this difference in behaviour of vector spaces and subspaces? The original code likely worked for halfplanes when it was written and there is no reason for it to stop.

Looking at the file src/sage/structure/parent.pyx in the __contains__ function, it returns False because:

sage: type(r)
<class 'sage.geometry.toric_lattice_element.ToricLatticeElement'>
sage: r2 = SQ(r); r2
(1, 0)
sage: type(r2)
<class 'sage.modules.vector_rational_dense.Vector_rational_dense'>

and

sage: r2 == r
False

Now, should this return True? I am not sure how to fix this...

[mkoeppe]

comment:5

pushing these forward to 9.2

[mkoeppe]

comment:8

Setting new milestone based on a cursory review of ticket status, priority, and last modification date.