[petsc-users] Scatter parallel Vec to sequential Vec on non-zeroth process

[Peder Jørgensgaard Olesen]

Dear Junchao Zhang


I'm distributing a set of independent tasks over different processes, so I'm afraid sending everything to the zeroth process would rather thoroughly defeat the purpose of what I'm doing.


Med venlig hilsen / Best regards

Peder

________________________________
Fra: Junchao Zhang <junchao.zhang at gmail.com>
Sendt: 30. juni 2021 16:00:25
Til: Peder Jørgensgaard Olesen
Cc: Matthew Knepley; petsc-users at mcs.anl.gov
Emne: Re: [petsc-users] Scatter parallel Vec to sequential Vec on non-zeroth process

That should work. But VecScatterCreateToZero() is more efficient. So if possible, better refactor your code in such a way.

--Junchao Zhang

On Wed, Jun 30, 2021 at 7:13 AM Peder Jørgensgaard Olesen via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:

Dear Matt


Thank you for your reply. I'm guessing that the line

if (rank) N = 0;

should be changed to something like

if (rank != target_rank) N = 0;

such that an empty SEQVEC and scatter are created on each rank other than target_rank.


Med venlig hilsen / Best regards

Peder

________________________________
Fra: Matthew Knepley <knepley at gmail.com<mailto:knepley at gmail.com>>
Sendt: 30. juni 2021 13:58:49
Til: Peder Jørgensgaard Olesen
Cc: petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>
Emne: Re: [petsc-users] Scatter parallel Vec to sequential Vec on non-zeroth process

On Wed, Jun 30, 2021 at 6:49 AM Peder Jørgensgaard Olesen via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:

Hello


I have a parallel vector, and I'd like to copy its data to a sequential vector located on a given process that is not necessarily the 0th process, so using VecScatterCreateToZero wouldn't do here.


How might one approach this?

The function is very short: https://www.mcs.anl.gov/petsc/petsc-current/src/vec/is/sf/interface/vscat.c.html#VecScatterCreateToZero
Just go in and replace '0' by the rank you want.

  Thanks,

     Matt

Med venlig hilsen / Best Regards


Peder Jørgensgaard Olesen

PhD Student, Turbulence Research Lab

Dept. of Mechanical Engineering

Technical University of Denmark

Koppels Allé

Bygning 403, Rum 105

DK-2800 Kgs. Lyngby


--
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://www.cse.buffalo.edu/~knepley/<http://www.cse.buffalo.edu/~knepley/>
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