David Roberts's profile - activity

@eric_g thanks for pointing that out.

In SageManifolds, coördinates are defined by means of charts and transition functions. For instance, I understand one can define a sphere by giving two charts and the usual transition arising from stereographic projections. But a sphere can also come with its own coordinates by being defined as a variety. Is there a way (or even a nice way!) to reconcile these two views when working with locally defined objects? For instance, I might have a function on a manifold that vanishes in some way, which when defined on charts is obvious, but when defined on the subvariety one needs to apply the defining equation(s) to see this. Other properties defined via equations in function rings (or other rings of sections of sheaves or bundles) are similar.

There's the related question http://ask.sagemath.org/question/9297... which asks specifically for the case of Lie algebra-valued forms.

I know one can work with real differential forms using SageManifolds, but what are the chances one can use out of the box code to extend to values in some vector space, or better, algebra? I'm thinking matrix Lie algebras, so one could work quite concretely, rather than over some abstract module.

I'd upvote, but I've not got the required karma. Virtual +1 from me, then.

I'm new to Sage and only beginner experience in python, so there may be something obvious I'm missing.

I'm trying to create, initially, some plots using Tachyon in SMC. I cut and pasted Niles Johnson's code at this question, namely

sage: f = lambda t: (t,t^2,t^3)
sage: t = Tachyon(camera_center=(5,0,4))
sage: t.texture('t')
sage: t.light((-20,-20,40), 0.2, (1,1,1))
sage: t.parametric_plot(f,-5,5,'t',min_depth=6)
sage: t.show(verbose=True)

and I get the following error

tachyon /projects/6e9b9fc6-5d3c-4c2a-a57f-b5fe78a365fd/.sage/temp/compute2dc1/22136/tmp_Iy4Cih.dat  -format PNG  -o /projects/6e9b9fc6-5d3c-4c2a-a57f-b5fe78a365fd/.sage/temp/compute2dc1/22136/tmp_weeBQD.png   ; rm -f "/projects/6e9b9fc6-5d3c-4c2a-a57f-b5fe78a365fd/.sage/temp/compute2dc1/22136/tmp_Iy4Cih.dat"
Error in lines 6-6
Traceback (most recent call last):
  File "/projects/6e9b9fc6-5d3c-4c2a-a57f-b5fe78a365fd/.sagemathcloud/sage_server.py", line 864, in execute
    exec compile(block+'\n', '', 'single') in namespace, locals
  File "", line 1, in <module>
  File "/usr/local/sage/sage-6.3.beta6/local/lib/python2.7/site-packages/sage/plot/plot3d/tachyon.py", line 339, in show
    os.system('%s %s 2>/dev/null 1>/dev/null &'%(sage.misc.viewer.png_viewer(), filename))
NameError: global name 'sage' is not defined

What should I do? It doesn't seem related to anything in the code used.