Jeremy Martin's profile - activity

Thanks. I knew this was what was going on but did not know the systematic way to handle it. Your last suggestion (cast it to the symbolic ring) is exactly what I was looking for.

How can you specify an integral with a constant integrand? For example, I know that

f = x
f.integrate(x,0,1)

works fine, but

f = 1
f.integrate(x,0,1)

doesn't, since the Integer class has no integrate() method. (Should it?) I can get around this with something like

f = x-x+1
f.integrate(x,0,1)

but that seems awfully kludgey.

I often use the SageMathCloud in the classroom. I would like to hide the toolbars to have more room for the math. I know I can hide the User and Project menus by clicking on the little X at the right, and I have unchecked the "Extra Button Bar" in my settings. Is there also a way to hide the other toolbar (with buttons like Run, Stop, Restart, etc.)?

I guess I can just use line3d() instead.... but maybe this error indicates something else is going on.

The following code (straight from http://doc.sagemath.org/html/en/refer...) does not work in the SageMath Cloud, at least not for me:

from sage.plot.plot3d.shapes2 import Line
Line([(i*math.sin(i), i*math.cos(i), i/3) for i in range(30)], arrow_head=True)

The result is a long error message ending with "TypeError: 0 is not JSON serializable". Am I doing something wrong?

Update: Having read http://ask.sagemath.org/question/2632..., I tried e = 1/10 and got the same error. Of course

parametric_plot3d( [b*t/e, -a*t/e, f(b*t/e,-a*t/e)], [t,-1,1], color="yellow", size=15 )

will do what I want, but there still seems to be an underlying problem with parametric_plot3d.

I'm working in the SageMath Cloud. The code block

x,y,t = var('x,y,t')
f = lambda x,y: x*abs(y)/sqrt(x^2+y^2) if (x,y)<>(0,0) else 0
a,b = 1,6
e = 0.1
parametric_plot3d( [b*t, -a*t, f(b*t,-a*t)], [t,-e,e], color="yellow", size=15 )

produces an error message:

error rendering 3d scene -- error downloading /blobs/682b952d-d577-45ce-98ff-4e7a06ddad32.sage3d?uuid=682b952d-d577-45ce-98ff-4e7a06ddad32

But if I change the fourth line to e = 1, then it works just fine.

A similar error was reported in http://ask.sagemath.org/question/2730..., but the fix there was easier.

Thanks. I did not know about the valuation() function before this.

@Nathann: Done.

@rws: Yes, it is not a bug, and I was able to do what I needed to do, but from an end-user standpoint, it would be better if the log() function did not require the user to distinguish between an integer and a Sage integer - most mathematicians would not think that there could be two kinds of integers!

I recently installed Sage 6.7 from source on my home computer, running OSX 10.9 (Mavericks). It is sloooooow. Just starting Sage from a terminal window takes a good two minutes; something simple like using the ? feature can take up to a minute; and serious power computation is hopeless. My computer has plenty of RAM and disk space, so I don't think that's the problem. I had the same problems with the previous version (5.something), but on other computers the performance is much better. I would be very grateful for suggestions about how to speed things up, particularly from others who have encountered this issue. Thanks!

I am working with a bunch of lists whose lengths are all powers of 2. I'd like to be able to extract the power by taking the base-2 log of the length. However, Sage wasn't able to simplify an expression like log(len(L),2), because apparently len() returns the wrong kind of integer:

sage: A=list(range(8))
sage: len(A)
8
sage: log(len(A),2)
log(8)/log(2)
sage: log(8,2)
3
sage: type(len(A))
<type 'int'>
sage: type(8)
<type 'sage.rings.integer.Integer'>
sage: log(Integer(len(A)),2)
3

This is the first math function I've come across that seems to care about the distinction between these two kinds of integers, and it would be nice if it didn't, since it took me quite a while to figure out why Sage wouldn't simplify an expression like log(len(A),2).

Done. Thanks; I'm new here and didn't know that.

The standard definition of a simplicial complex requires that it contain the empty face. However, sometimes one needs to distinguish between the complexes {} (the "void complex") and {{}} (the "irrelevant complex"). This comes up, e.g., when working with relative complexes or doing combinatorial commutative algebra (see, e.g., Stanley's Combinatorial Commutative Algebra, p.117, or Miller and Sturmfels, p.4). The SimplicialComplex class doesn't allow the void complex.

For example, if F is a facet of X then link_X(F) is the irrelevant complex, but if G is a nonface of X then link_X(G) is the void complex. However, the link method does not distinguish between the two, returning the irrelevant complex in both cases:

sage: X=SimplicialComplex([[1]])
sage: F=Simplex([1]); X.link(F)
Simplicial complex with vertex set () and facets {()}
sage: G=Simplex([2]); X.link(G)
Simplicial complex with vertex set () and facets {()}

This seems like a triviality but it would be helpful to have this distinction. What do others think?

The set_max method in MixedIntegerLinearProgram() does not seem to work correctly if the maximum value specified is 0. Specifically, the input....

Q = MixedIntegerLinearProgram();
xx = Q['xx'];
Q.set_min(xx,0);
Q.get_min(xx)

... returns null, but ....

Q = MixedIntegerLinearProgram();
xx = Q['xx'];
Q.set_min(xx,3);
Q.get_min(xx)

... works fine. Anyone know what's going on here?