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[sage-devel] Re: problem with complex_plot and real_part Burcin Erocal Fri Jun 26 06:00:29 2009

On Fri, 26 Jun 2009 08:27:44 -0300
Golam Mortuza Hossain <[EMAIL PROTECTED]> wrote:

> 
> Hi
> 
> On Thu, Jun 25, 2009 at 11:31 PM, Nick
> Alexander<[EMAIL PROTECTED]> wrote:
> >
> > Can someone verify that this is a bug?  Any hope a fix?  (This is
> > with sage-4.0.2 on sage.math.)
> >
> > {{{
> > sage: complex_plot((x^2 + I).sqrt().real_part(), (-2, 2), (-2, 2))
> > ---------------------------------------------------------------------------
> ...
> > RuntimeError: cannot find SFunction in table
> > }}}
> 
> It seems, its not just complex_plot issue. It is happening for other
> plots. For example,  the following works fine in 3.4 but fails with
> the same error in 4.0.2
> -----
> sage: x,y=var('x,y'); plot3d( log(x+I*y).imag(), (x,-2,2), (y,-2,2))
> ...
> RuntimeError: cannot find SFunction in table
> -----

sage: %debug
> /home/burcin/sage/sage-4.0.2.rc0/expression.pyx(3115)sage.symbolic.expression.Expression.operator
> (sage/symbolic/expression.cpp:15268)()

ipdb> u
> /home/burcin/sage/sage-4.0.2.rc0/local/lib/python2.5/site-packages/sage/symbolic/expression_conversions.py(206)__call__()
    205 
--> 206         operator = ex.operator()
    207         if operator is None:

ipdb> print ex
arctan2(real_part(y) + imag_part(x), real_part(x) - imag_part(y))


Both of these fail because Sage doesn't define a symbolic arctan2
function. There is instead a simple wrapper around arctan in
sage/functions/trig.py:

sage: arctan2(x,y)
arctan(x/y)

It's possible that this worked on 4.0, and I broke it with #6244.


I opened a ticket: 

http://trac.sagemath.org/sage_trac/ticket/6421


I don't think I will have time to fix this in the next few days. Feel
free to replicate one of the Function_* classes in
sage/functions/trig.py to define a new symbolic function called
arctan2, with ginac conversion atan2.


Thanks.

Burcin

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