[petsc-users] Question about TSComputeRHSJacobianConstant

[Matthew Knepley]

On Wed, May 22, 2019 at 3:28 PM Sajid Ali via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Hi Hong,
>
> Looks like this is my fault since I'm using -ksp_type preonly -pc_type
> gamg. If I use the default ksp (GMRES) then everything works fine on a
> smaller problem.
>
> Just to confirm,  -ksp_type preonly is to be used only with direct-solve
> preconditioners like LU,Cholesky, right ?
>

It depends what you want. preconly just applies the PC once. It could be
that you just want MG applied once, but
you have to know that you might not get residual reduction you want unless
your system has certain characteristics.

   Matt


> Thank You,
> Sajid Ali
> Applied Physics
> Northwestern University
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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