[petsc-users] KSPAGMRES Question

Frank Bramkamp bramkamp at nsc.liu.se
Tue Aug 2 12:18:56 CDT 2022

Dear PETSc team,

I have seen that there is the KSP method: KSPAGMRES,
https://petsc.org/release/docs/manualpages/KSP/KSPAGMRES.html <https://petsc.org/release/docs/manualpages/KSP/KSPAGMRES.html>

I wanted to test this method, as it also seems to reduce the amount of MPI communication, compared
to the standard GMRES. 

I supposed that the class is called “KSPAGMRES”.
But in the include files petscksp.h and petsc/finclude/petscksp.h 
there is no definition for KSPAGMRES, just KSPDGMRES.

I wonder if the definition KSPAGMRES is simply missing, or do I have to call
DGMRES and set another option for AGMRES ?!

The standard GMRES has the problem that MPI_Allreduce gets expensive for 2048 cores.
Therefore I wanted to see, if AGMRES has a bit less communication, as this is mentioned in the description
of the method. 

Greetings, Frank Bramkamp

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