[petsc-users] PETSc MPI world question

[Matthew Knepley]

On Fri, May 29, 2026 at 12:59 PM Y. Joseph Zhang via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Works like a charm; I actually mistakenly put that statement just after
> InitializePETSc (should be before)...
>
> While I have you there: we've migrated make system to cmake (which is
> needed for ESM coupling). I understand older versions of PETSc do not
> support cmake. Is it still the case?
>

We generate  $PETSC_DIR/share/petsc/CMakeLists.txt in order to support
inclusion in CMake builds. However you still build PETSc itself the same
way.

  Thanks,

     Matt

Thanks!
>
>
> -Joseph
>
>
>
> Joseph Zhang
>
> Office: (804) 684 7464 (note the new number)
>
> Web: schism.wiki
>
>
> ------------------------------
> *From:* Junchao Zhang <junchao.zhang at gmail.com>
> *Sent:* Friday, May 29, 2026 11:25 AM
> *To:* Y. Joseph Zhang <yjzhang at vims.edu>
> *Cc:* petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
> *Subject:* Re: [petsc-users] PETSc MPI world question
>
>
> *[EXTERNAL to VIMS received message]*
>
> Hi Joseph,
>   You can assign your compute world to PETSC_COMM_WORLD, see details at
> https://urldefense.us/v3/__https://petsc.org/release/manualpages/Sys/PETSC_COMM_WORLD/__;!!G_uCfscf7eWS!bkqAu8Q1t-AlYGS4WJgEpG8rAD96wdUJQiyAnNFK0wpC4F4gOdHelLm_HiR990Ud0ld3b27Q1KS_M0yTEa04$ 
> <https://urldefense.us/v3/__https://petsc.org/release/manualpages/Sys/PETSC_COMM_WORLD/__;!!G_uCfscf7eWS!Z6_GNPIsRXNJX3U0sds166hfOGlL3_ZMGpke19RG776xJfoij_WU08GDEp2F2nzek-QJwJqm1NNKc5L1UbPxwCk$>
>
> --Junchao Zhang
>
>
> On Fri, May 29, 2026 at 10:06 AM Y. Joseph Zhang via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
>
> Hi:
>
> We've been using PETSc solvers in our code for many years. A few years ago
> we changed the I/O method to improve efficiency, by reserving dedicated
> 'scribe' MPI processes. This entails the partitioning of MPI_COMM_WORLD
> into 2 worlds (1 for compute and the other for I/O).
>
> Is there a way to ask PETSc to use compute world only? Otherwise we'd get
> a lot of errors.
>
> Thank you for the great tool for the community!
>
>
>
> -Joseph
>
>
>
> Joseph Zhang
>
> Office: (804) 684 7464
>
> Web: schism.wiki
>
>
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://urldefense.us/v3/__https://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!bkqAu8Q1t-AlYGS4WJgEpG8rAD96wdUJQiyAnNFK0wpC4F4gOdHelLm_HiR990Ud0ld3b27Q1KS_MwpT9Tw_$  <https://urldefense.us/v3/__http://www.cse.buffalo.edu/*knepley/__;fg!!G_uCfscf7eWS!bkqAu8Q1t-AlYGS4WJgEpG8rAD96wdUJQiyAnNFK0wpC4F4gOdHelLm_HiR990Ud0ld3b27Q1KS_M6gJyfjA$ >
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