On Oct 9, 7:46 am, "ma...@mendelu.cz" <ma...@mendelu.cz> wrote:
> Hello,
>
> trying to fix desolve_laplace as described
> athttp://groups.google.cz/group/sage-support/browse_thread/thread/b6f6b...
>
> It is continuation of tickethttp://trac.sagemath.org/sage_trac/ticket/6479
> which has been (hope) solved.
>
> The temporary code ishttp://user.mendelu.cz/marik/temp/desolvers.py
> and it has been tested on equations like equations on the bottom of
> this post.
>
> I have still a problem: I do not know how to get sage representation
> of 'at(....)
>
> current desolve_laplace produce (via maxima) something like
> "x*%e^x*('at('diff('f(x),x,1),x=0))-'f(0)*x*%e^x+'f(0)*%e^x"
>
> If I do
> A=maxima("'at('diff('f(x),x,1),x=0)")
> A.sage()
>
> I expect the corresponding Sage expression but I get errors.
Ah, but there IS no corresponding Sage expression! That's the kicker.
See trac #385, as well as #3914 which would also be solved by it. So
this has been around a long time.
Ticket #385 is on my to-do list, and since you are interested, I can
try to get around to it soon. Or if you have a good solution at hand,
you can do it. See also
http://groups.google.com/group/sage-support/browse_thread/thread/d7520e53b492f878/f701fe54bac7c367?q=
- kcrisman
>
> As a result, the new desolve_laplace cannot be used to solve second
> order ODE without initial conditions.
>
> Can you help me to came over this step? Thank you.
>
> Robert Marik.
>
> btw: another improvement od desolve_laplace is, that it removes
> initial conditions after solving IVP, in the previous version initial
> condition persisted in the maxima session - see the Warming message
> after desolve_laplace?
>
> ---------------------------------------------------------------
> Test equations for new desolve_laplace:
>
> u=function('u',x)
> print "*******-----------"
> eq = diff(u,x,x) + u == 0
> #A=desolve_laplace(eq,u)
> #print A
>
> A=desolve_laplace(eq,u,ics=[0,1,2])
> print A
>
> eq = diff(u,x) - exp(-x) - u == 0
> A = desolve_laplace(eq,u)
> print A
> A=desolve_laplace(eq,u,ics=[0,3]).expand()
> print A
> A=desolve(eq,u,ics=[0,3]).expand()
> print A
> A=desolve_laplace(eq,u).expand()
> print A
>
> print "*******"
> eq= diff(u,x) - exp(-x) - u == 0
> A=desolve_laplace(eq,u,ics=[0,3])
> print A
> eq= diff(u,x) - exp(-x) - u == 0
> A=desolve_laplace(eq,u)
> print A
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