Hi all,
Technically, this is not a Sage problem, but I figured I would post it
here anyway since others might have run into the same problem, and I'm
also trying to solve the problem using some Sage/python trickery.
The problem concerns the use of symbolic constants such as pi in
numerical integration with desolve_rk4. The following code is adapted
from the manual page for desolve_rk4 -- note especially the constant
pi in the specification of the ODE:
x, y = var('x y')
desolve_rk4(x*y*(2-y) + pi, y, ics=[0, 1], end_points=1, step=0.5)
and raises the following error:
TypeError: Error executing code in Maxima
CODE:
sage1 : rk(%pi-x*(y-2)*y,y,1,[x,0,1,0.500000000000000]) $
Maxima ERROR: Inconsistent set of equations and variables
This same error occurs whenever you have an ODE with pi in it, no
matter how simple. The error persists when directly running this
command in Maxima, but works fine (both in Sage and Maxima) when
manually replacing pi by 3.14... Since I don't know any Maxima, I
have no idea of what the problem could be or where to look.
So, I was wondering if there is a way to have Sage replace the %pi
when invoking Maxima by the corresponding numerical value? I guess I
could store my ODE in a string and use a regular expression to get rid
of any pi's myself, but that seems very inelegant. Is there anything
you would recommend?
Thanks a lot,
Joris
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