[petsc-users] MKL Pardiso Solver Execution Step control

[Matthew Overholt]

Barry,

What I should have said was that I wanted to control when it does the
"Analysis" (phase 11), not Factoring (phase 22).  We are solving the heat
conduction equation, which makes for a nearly linear system; the
non-linearity only enters through the material properties dependence on
temperature, which is usually weak.  We use the direct approach with
several fixed point iterations to get the solution.  We have found (in our
non-PETSc code) that a lot of time can be saved, particularly when
unsteady, by judiciously choosing when to (re)do the Analysis.  Typically
we do the Analysis on output time steps when unsteady, and just for the
first fixed point iteration when steady.

Matt...

On Tue, Jun 5, 2018 at 5:03 AM, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>
> > On Jun 4, 2018, at 10:32 PM, Matthew Overholt <overholt at capesim.com>
> wrote:
> >
> > Hello,
> >
> > I am using KSP in KSPPREONLY mode to do a direct solve on an A*x = b
> system, with solver algorithms MUMPS, CPardiso and Pardiso.  For Pardiso,
> is it possible to control the solver execution step (denoted "phase" in
> Intel's docs)?  I would like to be able to control when it refactors as one
> can when calling it directly.
>
>    Matt,
>
>      This is handled automatically by PETSc. If the matrix entries change
> than PETSc will automatically call the correct code to perform a new
> numerical factorization; if the matrix entries are not changed then it will
> not refactor the matrix. I am not sure if it makes sense for a user to be
> setting different phase values since it is handled automatically. Could you
> explain your exact use case where you would like to control the phase
> variable directly?
>
>     Barry
>
>
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