> On Jul 27, 2018, at 3:26 AM, Pierpaolo Minelli <pierpaolo.mine...@cnr.it>
> wrote:
>
>
> Finally, I have a question. In my simulation I solve the two systems at each
> step of the calculation, and it was my habit to use the following option
> after the first resolution and before solving the system in the second time
> step:
>
> call KSPSetInitialGuessNonzero(ksp,PETSC_TRUE,ierr)
>
> Since this option was incompatible with the use of MUMPS or SuperLU_Dist, I
> commented on it and noticed, to my surprise, that iterative methods were not
> affected by this comment, rather they were slightly faster. Is this normal?
> Or do I use this command incorrectly?
Presuming this is a linear problem?
You should run with -ksp_monitor_true_residual and compare the final
residual norms (at linear system convergence). Since KSP uses a relative
decrease in the residual norm to declare convergence what you have told us
isn't enough to determine if one is converging "faster" to the solution then
the other.
Barry
>
> Thanks
>
> Pierpaolo
>
>> Il giorno 23 lug 2018, alle ore 15:43, Mark Adams <mfad...@lbl.gov> ha
>> scritto:
>>
>> Note, as Barry said, GAMG works with native complex numbers. You can start
>> with your original complex build and use '-pc_type gamg'.
>> Mark
>>
>> On Mon, Jul 23, 2018 at 6:52 AM Pierpaolo Minelli <pierpaolo.mine...@cnr.it>
>> wrote:
>>
>>
>> > Il giorno 20 lug 2018, alle ore 19:58, Smith, Barry F.
>> > <bsm...@mcs.anl.gov> ha scritto:
>> >
>> >
>> >
>> >> On Jul 20, 2018, at 7:01 AM, Pierpaolo Minelli <pierpaolo.mine...@cnr.it>
>> >> wrote:
>> >>
>> >> Hi,
>> >>
>> >> in my code I have to solve both a system in the field of real numbers and
>> >> in the field of complex numbers.
>> >> My approach has been as follows.
>> >> First I configured PETSc with the --with-scalar-type=complex option.
>> >> Using this option I have unfortunately lost the possibility to use the
>> >> two preconditioners ML and Hypre.
>> >
>> > You should still be able to use the PETSc PCGAMG algebraic multigrid
>> > solver. Have you tried that? If there are issues let us know because we
>> > would like to continue to improve the performance of PCGAMG to get it to
>> > be closer to as good as ML and hypre.
>> >
>> > Barry
>> >
>>
>> I will try to convert, as suggested by Matthew, my complex system in a
>> system twice as large in real numbers. When i finish, i will try to use ML,
>> Hypre and GAMG and i let you know if there are any performance differences.
>>
>> Thanks
>>
>> Pierpaolo
>>
>>
>> >> I later created two subspaces of Krylov and tried to solve the two
>> >> systems as I used to when solving the only equation in the real numbers
>> >> field.
>> >> In order to correctly solve the system in the field of real numbers I had
>> >> to transform the coefficients from real to complex with an imaginary part
>> >> equal to zero.
>> >>
>> >> Is there a possibility to use a different and better approach to solve my
>> >> problem?
>> >>
>> >> Perhaps an approach where you can continue to use ML and Hypre for system
>> >> solving in the real numbers field or where you don't need to use complex
>> >> numbers when real numbers would actually suffice?
>> >>
>> >> Thanks in advance
>> >>
>> >> Pierpaolo
>> >>
>> >
>>
>
