On Oct 3, 6:10 pm, "ma...@mendelu.cz" <ma...@mendelu.cz> wrote:
> On 3 říj, 23:22, "ma...@mendelu.cz" <ma...@mendelu.cz> wrote:
>
>
>
> > I have not enought skill in Python, Sage, hg and related thinks. Is
> > there any person interested in the problem, which sould like to try
> > this?
>
> The following code works in Sage
>
> y=function('y',x)
> k1,k2=var('k1 k2')
> x0,y0,y1=0,1,2 # initial conditions y(x0)=y0 and y'(x0)=y1
> eq=diff(y,x,2)+3*diff(y,x)-4*y==exp(x)
> A=desolve(eq,y)
> sols_k=solve([y0==A.subs(x=x0),y1==diff(A,x).subs(x=x0)],
> [k1,k2],solution_dict=True)
> A=A.subs(k1=sols_k[0][k1]).subs(k2=sols_k[0][k2])
> A
>
> So I think that the following lines from definition of desolve in Sage
> (obtained from desolve??)
>
> ics = to_eqns([ivar, dvar, dvar.derivative(ivar)], ics)
> soln = soln.ic2(*ics)
>
> could be replaced by something like
>
> sols_k=solve([ics[1]==soln.subs(x=ics[0]),ics[2]==diff(soln,x).subs
> (x=ics[0])],\ [k1,k2],solution_dict=True)
> soln=soln.subs(k1=sols_k[0][k1]).subs(k2=sols_k[0][k2])
>
It sounds like you understand it at least as well as anyone responding
so far. Why not give it a go? I never thought I would know enough
about Python or Mercurial either. If you don't have a Trac account,
email William privately for one, and then you can log this as a ticket
and create a patch. In the meantime the documentation for doing very
basic patches is pretty good in the developer's guide, which I think
is linked on sagemath.org as well as in the documentation included
with your Sage installation.
Good luck!
- kcrisman
> and this should work at least for linear second order ODE, where IVP
> has unique solution (I am not sure if desolve solves also some
> nolinear ODE's). Perhaps with a test that the solution sols_k exists
> and is unique (which is IMHO allways true for linear ODE's).
>
> Yours sincerelly
>
> Robert Marik
>
>
>
> > Robert Marik
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