Thanks Robert, this seems to be the problem. I wish I were a lisp
programmer so that I could dive into Maxima and put in a call to
coerce-float-fun myself, but while I'm eager to tinker with this, I'm
not sure I can be succesful in a reasonable amount of time.
In the meantime, I will write my own little RK4 routine in python --
while browsing the mailing list yesterday I read about "fast_float",
so I have good hopes that the result will be fast. Sage is so
powerful!
Thanks a lot for your time,
Joris Vankerschaver
On 19 apr, 20:52, Robert Dodier <robert.dod...@gmail.com> wrote:
> Looks like the rk function in Maxima doesn't try hard enough to
> float-ify its argument. I haven't looked at the code, but
> maybe rk can call COERCE-FLOAT-FUN to construct a
> function to evaluate the expression. At least that would
> bring it into line with other Maxima functions which
> evaluate expressions to numbers (e.g. plotting, quadpack).
>
> Follow-ups to the Maxima mailing list. I've appended
> the original message below.
>
> best
>
> Robert Dodier
>
> PS.
>
> On Apr 19, 8:38 am, jvkersch <joris.vankerscha...@gmail.com> wrote:
>
>
>
> > 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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