On Tuesday, April 16, 2013 8:54:35 PM UTC-4, P Purkayastha wrote:
>
> On 04/16/2013 09:57 PM, GaryMak wrote:
> > Hi
> >
> > I am trying to use plot functions for the first time in sage - apologies
> > if this is a dumb question for a change.
> >
> > I have a square matrix M of fixed complex numbers which are then all
> > multiplied by a different phase depending on which column they are in.
> > (In the 2x2 example below M=[a,b;c,d] and column 1 is multiplied by
> > exp(i*theta) and column 2 is multiplied by exp(i*phi) ). I then take
> > another fixed matrix A away from M and take f=det(M-A).abs() as my
> > output. I have explicitly written this formula for A = [1,1;0,0] below.
> > So the function I would like to plot is f as a function of theta and phi
> > (in this case).
> >
> > a = 1/2
> > b = - i/3
> > c = 1/4
> > d = i/5
> > theta, phi = var('theta,phi')
> > f(theta,phi) = ( (a*exp(i*theta)-1)*d*exp(i*phi) -
> > (b*exp(i*phi)-1)*c*exp(i*theta) ) . abs()
> > plot3d(f, (theta,0,pi), (phi,0,pi))
> >
> > No matter how I try to do this, even if I explicitly write out the
> > complex conjugates of each element, I get what for me is a record-length
> > screed of error stuff ending in 'TypeError: unable to coerce to a real
> > number', originating in the command 'plot3d(...etc...)'. I have attached
> > a text file with the full output of one of my attempts.
> >
> > I can see that in a way I am asking a lot of the interpreter; but then
> > again I feel I have explicitly made the thing real by the time it gets
> > to be an input for the plot3d function.
> >
> > Is there any way around this, or do I have to start writing complexes as
> > a+bi etc and do it the hard way?
> >
> > Many thanks
> >
> > Gary
>
> The problem is actually in the conversion of your function to a
> fast_float() version of the function. Apparently, it fails for symbolic
> "complex" functions (which are not really complex) even in this trivial
> example:
>
> f(theta, phi) = (theta + i * phi).abs()
> ff = fast_float(f, 'theta', 'phi')
>
See http://trac.sagemath.org/sage_trac/ticket/13355
and http://trac.sagemath.org/sage_trac/ticket/5572
ppurka, can you try the patch at #13355 to see if that helps in this case?
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