Dear Robert,
Thanks a lot for the suggestion. After typing in "ode_solve", the tab-
completion guided me to the class "ode_solver", which also works like
a charm. This is the reason for my late reply: I was so glad to get
everything working that I lost all track of time...
I know this is not the place for a panegyric on Sage, but I've been
playing around with Sage for only a week and it is amazing. I'm
behind on all my work while I'm redoing all my code in Sage, and I
even wrote a small differential forms package, all in one week :)
Thanks a lot!
Joris
On 20 apr, 15:20, "ma...@mendelu.cz" <ma...@mendelu.cz> wrote:
> On 20 dub, 09:39, jvkersch <joris.vankerscha...@gmail.com> wrote:
>
> > 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!
>
> You may also try Octave or ode_solve. (run ode_solve? command to see
> the help)
>
> Robert
>
>
>
> > 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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