[petsc-users] Question on TS

[Jed Brown]

On Wed, Dec 26, 2012 at 1:00 AM, amlan barua <abarua at iit.edu> wrote:

> Hi,
> Greetings to the team! I am currently using PETSc for my research. Here is
> a brief description of my problem and my query
> a) I have a set a points distributed on a 3 dimensional lattice.
> b) Corresponding to each point in this set, 7 odes are defined.
> c) Of these 7 odes, 6 are uncoupled but one is coupled to nearest
> neighbors.
>

I suggest not optimizing for "missing" coupling to start with. We can do
the optimization in the solver, perhaps by splitting the DMDA into the
local and coupled parts.


> d) To integrate the odes I am using PETSc's DMDA and TS. But my
> application needs implicit as well as locally high order solver. I am
> looking for an implicit RK4 type method. Does PETSc have an IRK4 support or
> equivalent?
>

If you are happy with a diagonally implicit method, you can use TSARKIMEX
(these integrators can be IMEX, but can also do any diagonally implicit
method).

If you want a fully implicit RK (like Gauss, Radau IIA, etc) then all
stages are coupled together. Those methods are not currently implemented in
PETSc, though you could implement it either as a new TS implementation
(good for code reuse; you can do this outside of PETSc, but the code you
write is like library code) or manually using SNES (not reusable).


> e) Suppose I want to build my own implicit time stepper. Should I imitate
> ex2.c of SNES solver?
> Thanks
> Amlan
> IISER Pune, India
>
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