[petsc-users] MKL Pardiso Solver Execution Step control

[Matthew Knepley]

On Tue, Jun 5, 2018 at 11:08 AM, Matthew Overholt <overholt at capesim.com>
wrote:

> Yes to Matthew - not repeating Phase 1: Fill-reduction analysis and
> symbolic factorization .  Numerical factoring is required because the
> matrix values have changed (although only slightly) as well as the RHS.
>
> We are using KSPPREONLY with Picard iterations.  Thank you, Barry, for the
> KSP*Preconditioner calls I wasn't aware of.
>
> It sounds like PETSc and/or Pardiso automatically determines whether Phase
> 1 is required or not, but if we want to force a new Phase 1 (such as in a
> long unsteady run), then I suppose we could just destroy KSP and remake it.
>

Hmm, we have PetscErrorCode MatGetNonzeroState(Mat mat,PetscObjectState
*state). We probably should add MatIncrementNonzeroState().

   Matt


> Matt...
>
> Matt Overholt
> CapeSym, Inc.
> (508) 653-7100 x204
> overholt at capesim.com
>
> On Tue, Jun 5, 2018 at 10:40 AM, Matthew Knepley <knepley at gmail.com>
> wrote:
>
>> 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/>
>>
>
>


-- 
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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