[petsc-users] PC_SUBPC_ERROR with -pc_factor_zeropivot

[Matthew Overholt]

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
>
>
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