[petsc-users] PC_SUBPC_ERROR with -pc_factor_zeropivot

[Matthew Knepley]

On Mon, Jul 9, 2018 at 11:05 AM Matthew Overholt <overholt at capesim.com>
wrote:

> The -sub_pc_factor_zeropivot <value> option works, but since this is for a
> commercial code I don't want users to have to type that every time.
>
> Is there an equivalent call to
> PCFactorSetZeroPivot()
> for the block Jacobi method (like PCSubFactorSetZeroPivot())?  I can't
> find it.
>
> Instead, does one need to call
> PCBjacobiGetSubKSP()
> and then loop over every block, calling
> KSPGetPC()
> PCFactorSetZeroPivot()
> on each block?  That seems a little tedious, but if that is the correct
> approach I'll do it.
>

Yes, that is the API approach. As you can see, for composed solvers its not
a great option. How about
putting


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscOptionsSetValue.html

in the code?

  Thanks,

    Matt


> Thanks,
> Matt Overholt
>
> On Mon, Jul 9, 2018 at 10:17 AM, Matthew Overholt <overholt at capesim.com>
> wrote:
>
>> Thanks, Matt, that option works perfectly, and explains the -ksp_view
>> output.
>>
>> Much appreciated!
>>    Matt...
>>
>> On Fri, Jul 6, 2018 at 6:25 PM, Matthew Knepley <knepley at gmail.com>
>> wrote:
>>
>>> Default Case (zeropivot is 2.22045E-14):
>>>> mpiexec -n 1 ...
>>>> ==> ksp fails due to pcReason = PC_FACTOR_NUMERIC_ZEROPIVOT
>>>>
>>>> Reduced pivot case, n = 1:
>>>> mpiexec -n 1 ... -pc_factor_zeropivot 1E-15
>>>> ==> runs successfully
>>>>
>>>> Reduced pivot case, n > 1:
>>>> mpiexec -n 2 .. -pc_factor_zeropivot 1E-15
>>>> ==>  ksp fails due to pcReason = PC_SUBPC_ERROR
>>>>
>>>
>>> Okay, what is likely happening is that your preconditioner is actually
>>> Block-Jacobi/LU
>>> instead of parallel LU. Thus you would need
>>>
>>>   -sub_pc_factor_zeropivot 1e-15
>>>
>>>
>

-- 
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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