I've been graphing some 2D lattice polytopes using a trick I learned from
Andrey Novoseltsev a while ago: plot the polytopes in 3D, then rotate into
the xy plane for a two-dimensional image. I discovered that when I graph a
larger lattice polytope, the intersection of the x and y axes moves away
from (0,0). Is there a command to force the axes to intersect at the
origin? Or have I discovered a bug?
Here are some examples.
Here is code I ran yesterday at sagenb.org (using the Chrome browser in
Windows):
m = lattice_polytope.read_palp_matrix(r"""4 2
-1 0
1 -2
-1 5
1 5
""")
p = LatticePolytope(m)
pl = p.plot3d(show_vindices=False, show_points=False, edge_color="blue")
size = 4
for i in range(-size, size+1):
for j in range(-size, size+1):
pl += point3d((i,j,0))
pl.show(frame=False, axes=True)
Here is the resulting image:
http://www.flickr.com/photos/ursulageorges/7997105568/in/photostream
You'll see that the polytope appears to have a vertex at (-1,-1), when it
should have a vertex at (-1,0).
Today, sagenb.org is running slowly, so I tried the virtual version on my
Windows machine. I think it's a slightly earlier version of Sage (I
installed it last spring).
Here's code for the same polytope without blue dots on the integer points:
m = lattice_polytope.read_palp_matrix(r"""4 2
-1 0
1 -2
-1 5
1 5
""")
p = LatticePolytope(m)
pl = p.plot3d(show_vindices=False, show_points=True, edge_color="blue")
pl.show(frame=False, axes=True)
Here is the image that resulted. This time the axes don't even seem to be
passing through a point with integer coordinates!
http://www.flickr.com/photos/ursulageorges/7997110398/in/photostream
UAW
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