Sorry - at ease ...
If I name the plot PP or something then put just 'PP' in a different cell
from its definition, it shows up fine.
Thanks again for the help
Kind regards
Gary
On Wed, Apr 17, 2013 at 10:39 AM, GaryMak <garymako...@googlemail.com>wrote:
> Hi @ppurka - thank you very much as I would never have thought of that! -
> that certainly fixes the crashing problem - but I now have an even more
> bizarre problem, which is that plot3d does literally nothing! I have
> re-booted everything but it makes no difference. Here is my code:
>
> s = 4
> a=1/s
> b=1/s
> c=1/s
> d=i/s
> theta, phi = var('theta,phi')
> def f(theta,phi): return ( (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))
>
> I know that plot3d works in the same notebook() session say on examples
> from the SAGE Reference manual, and the function f as you defined it also
> works fine on individual (pairs of) angles ... does this code work on your
> computer?
>
> Thanks again
>
>
>
>
> On Wednesday, April 17, 2013 2:54:35 AM UTC+2, 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')
>>
>> One trivial workaround is to define your function to be a python
>> function. Somehow, it works. :)
>>
>> def f(theta,phi): return ( (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, phi))
>>
>>
>> --
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