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Apr 19, 2010, 10:38:09 AM4/19/10

to sage-support

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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URL: http://www.sagemath.org

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

--

To post to this group, send email to sage-s...@googlegroups.com

To unsubscribe from this group, send email to sage-support...@googlegroups.com

For more options, visit this group at http://groups.google.com/group/sage-support

URL: http://www.sagemath.org

Apr 19, 2010, 2:52:18 PM4/19/10

to sage-support, Maxima Mailing List

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.

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.

Apr 20, 2010, 3:39:41 AM4/20/10

to sage-support

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

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

Apr 20, 2010, 9:20:03 AM4/20/10

to sage-support

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!

>

the help)

Robert

Apr 21, 2010, 1:47:26 PM4/21/10

to sage-support

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

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

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