Bill's profile - activity

How can I tell sage to make a twitter post?

I'm trying to get sagemath to read from my USB port which has an arduino attached to it. The arduino is throwing a bunch of text to the serial port with address /dev/ttyUSB0

A preliminary Google search reveals that there is a python library pySerial which is designed to do just this. Can I make sagemath recognize this library somehow?

Thanks!

I can save a graphic I have created as a svg using the following command:

p.save('/home/so10b.svg')

However, my particular graphic is saved as a 39.5MB file, which is too large for my graphic editor to handle well. Saving as .ps creates a 20.4MB file.

In the end, I want a .png, but with particular printed dimensions and resolution. So:

What command will allow me to save a graphic in raster format with specific dimensions and resolution?

Is there a way to populate the face_list attribute of the result of parametric_plot3d without showing the plot itself? I am running a script to generate a lot of these surfaces, and I am not interested in closing the jmol window for each surface.

Thanks!

Perhaps it is because these polyhedra are degenerate?

OK. So, I've lost that original code which produced this error. However, I have noticed some new strange behavior when intersecting polyhedra and can give you specifics: a = Polyhedron([[1.0, 0.0, -0.7071067812], [0.5, -0.5, 0.0]]) b = Polyhedron([[-0.5,-0.5,0.0]]) c = Polyhedron([[0.0, -1.0, 0.7071067812], [0.5, -0.5, 0.0], [-0.5, -0.5, 0.0]]). a & b is empty, while (a & b) & c is 0-dimensional.

Right. Sorry. Each poly[i] is a polyhedron defined as a convex hull on some of the points from b.

@kcrisman OK. I included a definition of b. It's a dictionary containing the coordinates of the barycentric subdivision of a 3-simplex.

I have a dictionary of polyhedra which I want to consider various intersections and unions of. For now, my dictionary has four polyhedra in it. When running the following for loop:

v={} # contains coordinates of the tetrahedron, centered at (0,0,0)
v[1] = vector([1,0,-1/sqrt(2)])
v[2] = vector([-1,0,-1/sqrt(2)])
v[3] = vector([0,1,1/sqrt(2)])
v[4] = vector([0,-1,1/sqrt(2)])

V = {1,2,3,4}

b={} # will contain coordinates of vertices of the subdivision of the tetrahedron

for X in powerset(V):
  q = len(X)
  if q > 0:
    b[tuple(X)] = (1/q)*sum([v[i] for i in X])

poly_int = Polyhedron([b[key] for key in b.keys()]) # this is a tetrahedron containing
# all of my polyhedra
for i in [1,2,3,4]:
  poly_int = poly[i] & poly_int

I get a very nasty error:

AttributeError: 'Polyhedra_RDF_cdd_with_category.element_class'
object has no attribute '_Vrepresentation'

(The traceback for the error is quite long. I can include it if needed.)

Manually computing

poly[1] & poly[2] & poly[3] & poly[4]

gives the same error. HOWEVER, if instead I compute

(poly[1] & poly[2]) & (poly[3] & poly[4])

I get no errors. While this is a fine workaround for this particular case, I'm scripting these intersections and need some way to actually compute these intersections automatically. Using something like

poly[1].intersection(poly[2]) # etc.

doesn't help either. Any thoughts?

I was recently running a script I wrote to triangulate a polygon, and after a few hours sage crashed. I was left with the following messages:

/usr/local/bin/sage/local/bin/sage-sage: line 301: 20880 Killed                  sage-cleaner &>/dev/null
/usr/local/bin/sage/local/bin/sage-sage: line 301: 20881 Killed                  sage-ipython "$@" -i

What happened? What do these messages indicate?

I will look at that algorithm. Thanks.

Thanks for the suggestion. Unfortunately, I am working in a setting where taking the convex hull of the vertices of my polygon is not what I want to do. (My polygons have holes in them.)

If I feed sage a list of vertices, then the polygon() function can create a 2D polygon determined by visiting these edges in order (with self-intersections, repeated edges, holes, etc.).

Does sage have a built-in method to triangulate the resulting polygon? (It appears to me as though this is not the case.)

If not, I would love to see your homemade code to do this.

I figured it out. The .triangulate() function does exactly this.

Try this:

someTriangle = parametric_plot3d(t*(1-s)*v + s*w, (t,0,1), (s,0,1))

In general, if you want t to be in the interval [a(s), b(s)], just use t' = a(s) + t*(b(s) - a(s)) and let t range from 0 to 1. For example, to graph the function f(s,t) = 1 for s in [0,1] and t in [s^2, s]:

sage: var('s,t')
(s, t)
sage: parametric_plot3d([s,(s^2 + t*(s - s^2)),1], (t,0,1), (s,0,1))

And here's a more complicated example:

sage: var('s,t,x,y')
(s, t, x, y)
sage: f = sin(x)*cos(y)
sage: tprime = s^2 + t*(s - s^2)

The rectangular plot:

sage: parametric_plot3d([s,t,f(x=s,y=t)], (t,0,1), (s,0,1))

Change coordinates to plot only a part of the t range:

sage: parametric_plot3d([s,tprime,f(x=s,y=tprime)], (t,0,1), (s,0,1))

Thanks, Niles. I'm kicking myself now.

Is it possible to give parametric_plot3d parameter ranges where one parameter is a function of the other? For example, I would like the following command to execute and create a plot of a triangle in $\mathbb{R}^3$.

v = some vector
w = some other vector
someTriangle = parametric_plot3d(t*v + s*w, (t,0,1-s), (s,0,1))

Thanks!