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Solving system of ODE gets "ValueError"

asked 2017-07-15 18:16:48 -0500

xuesen_umd gravatar image

updated 2017-07-16 06:08:39 -0500

I'm trying to solve a system of ODE using desolve_system but get "ValueError":

t=var('t'); f=function('f')(t); g=function('g')(t);
de1 = diff(f,t) == f*sin(t);
de2 = diff(g,t) == 0;
desolve_system([de1, de2], [f,g])

gets:

Traceback (click to the left of this block for traceback)
...
ValueError: The name "+" is not a valid Python identifier

the problem seems to be sin(t) factor, without it the system solves with no problem. Also desolve(de1, f) has no problem. What is going on here?

Thanks in advance!

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Comments

Your equations are independent. Note that solving the equation one by one does work

sage: desolve(de1, f)
_C*e^(-cos(t))
sage: desolve(de2, g)
_C
vdelecroix gravatar imagevdelecroix ( 2017-07-16 06:11:19 -0500 )edit

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answered 2017-07-16 12:48:14 -0500

The problem comes from the fact that Sage is not able to understand Maxima's answer

f(_SAGE_VAR_t) = ilt((%i laplace(f(_SAGE_VAR_t), _SAGE_VAR_t, g2579 + %i)
 - %i laplace(f(_SAGE_VAR_t), _SAGE_VAR_t, g2579 - %i) + 2 f(0))/(2 g2579), g2579, _SAGE_VAR_t)

I opened the ticket #23445 to track the issue.

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Asked: 2017-07-15 18:16:07 -0500

Seen: 59 times

Last updated: Jul 16