[petsc-users] Question about TSSetRHSJacobian for linear time dependent problem

[Sajid Ali]

The form is u_t = A(t)u.

On Sun, Jan 27, 2019 at 4:24 PM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>
> > On Jan 25, 2019, at 4:51 PM, Sajid Ali via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> >
> > Hi,
> >
> > If I have a linear time dependent equation I'm trying to solve using TS,
> I can use :
> > TSSetProblemType(ts,TS_LINEAR);
> > TSSetRHSFunction(ts,NULL,TSComputeRHSFunctionLinear,NULL);
> > TSSetRHSJacobian(ts,A,A,YourComputeRHSJacobian, &appctx);
> >
> > If the matrix that's being evaluated by YourComputeRHSJacobian is such
> that the non-zero structure stays the same and only the diagonal changes
> with time, is there a way to optimize the function so that it doesn't
> create the whole matrix from scratch each time ?
>
> If it is a linear PDE u_t = A u  then how can A change with time? It
> sounds like it really isn't a linear problem?
>
>    Barry
>
> >
> > Naively I can make a dummy matrix and store the copy from t=0 and change
> the diagonal at each iteration but that unnecessarily doubles the memory
> consumption, is there a better way?
> >
> >
> > Thank You,
> > Sajid Ali
> > Applied Physics
> > Northwestern University
>
>

-- 
Sajid Ali
Applied Physics
Northwestern University
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