[petsc-users] Parallel sort in Petsc

[Antoine Côté]

Hi,

I need to compute the permutations to sort scalar values of a Vec object in decreasing order. I've been developing on a single process for now, using VecGetArrayRead() to extract the values and PetscSortRealWithPermutation() to get the permutations.

I would like to run the code on multiple processes. From these links, I can see it's an issue :
https://lists.mcs.anl.gov/pipermail/petsc-users/2013-November/019628.html
https://lists.mcs.anl.gov/pipermail/petsc-users/2009-June/004621.html

One work around I've been considering : get the max scalar value using VecMax() ; compute a scaling factor that makes this max value equals the largest integer value tolerated by PetscInt ; scale all values of Vec and convert them to integers ; use PetscParallelSortInt() ; inverse the scaling on (now sorted) integers values and convert them back to scalars.

This is only a patch really, the main issues being : (1) I would get a sorted Vec, not the permutations and (2) there would be a lost of information when converting scalars to int values.

Isn't there a way to parallel sort real values using Petsc?

Thank you very much!

Antoine Côté


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