[petsc-users] MKL Pardiso Solver Execution Step control

[Matthew Knepley]

On Tue, Jun 5, 2018 at 10:04 AM, Matthew Overholt <overholt at capesim.com>
wrote:

> Barry,
>
> What I should have said was that I wanted to control when it does the
> "Analysis" (phase 11), not Factoring (phase 22).
>

If you only change values in the matrix, but not the structure of the
matrix, PETSc will only repeat the numerical factorization,
not the symbolic factorization, which I think is what you want.

  Matt


> 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
>>
>>


-- 
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.caam.rice.edu/~mk51/>
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