[petsc-users] Suggestions for single process setup code

[Jasper Hatton]

Hi Barry,

Thanks! That answers my question.

Cheers,

Jasper

________________________________
From: Barry Smith <bsmith at petsc.dev>
Sent: Thursday, August 21, 2025 5:31 PM
To: Jasper Hatton <jasper.hatton at mail.utoronto.ca>
Cc: petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: Re: [petsc-users] Suggestions for single process setup code

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  As you note, the MPI linear solver server is for matrices whose entries are explicitly provided (so xAIJ sparse and dense) it doesn't have code that would help with shell matrices.

  You should write a parallel code, but have rank 0 do most of the work initially. You can have rank 0, for example, do the MatSetValues() calls.

   Any specific questions, feel free to ask.

   Barry

On Aug 21, 2025, at 3:42 PM, Jasper Hatton via petsc-users <petsc-users at mcs.anl.gov> wrote:

Hi,

I am looking for advice on using PETSc in a situation where I don't want the initial setup part of my application to run on multiple processes. The solution stage is taking up most of the time, so I would like to avoid making the setup stage a fully parallel code for now.

My solution stage takes a shell matrix, which includes an FFT as well as multiple sparse mat-vec products. So I was planning to use the rank zero process to setup the distributed FFT and put values into the distributed matrices, then execute KSPSolve on all ranks.

However, I see there is also the MPI linear solver server option. It seems mostly useful for cases where the input to KSPSolve is a sparse/dense matrix rather than a shell code. Is it something I should consider for my case?

This is meant to be an first step which can at least run well on a 2-socket node with many cores available, and eventually could be made a fully distributed code in the future.

Any advice would be apreciated!

Thanks,

Jasper

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