[petsc-users] KSPAGMRES Question

[Barry Smith]

  Ok, this is embarrassing, all the code is there and the documentation, but it is not wired up to be usable; I'm not sure how that happened. The code was contributed over two years ago, and I have no memory of why it would be there but not wired up. I wired it up and ran a simple test and got MPI errors, so I suspect that the code had serious bugs we did not understand and so was not wired up; 

  There are other pipelined GMRES KSPPGMRES and KSPPIPEFGMRES that are wired up and should be usable out of the box. Plus a pipelined bcgs. I suggest starting by trying those.



  Barry


> On Aug 2, 2022, at 12:18 PM, Frank Bramkamp <bramkamp at nsc.liu.se> wrote:
> 
> 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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