[petsc-users] Global numbering obtained via ISPartitioningToNumbering is inconsistent with the partitioning indexset

[Mohammad Mirzadeh]

Hi,

I am using  'ISPartitioningToNumbering' to generate new global numbering
from a partitioning indexset and I'm baffled at the following situation.
I'm debugging my code on a simple grid consisting of 81 grid points
partitioned among two processes. When I look into the partitioning indexset
(i.e. looking at the indecies via ISView) I can see that 40 points have
been assigned to proc 0 and 41 to processor 1. Isn't it true that when 81
points are distributed among two processors 41 should go to proc 0 and 40
to proc 1?

I have based my whole code on the assumption (verified before through
mailing list i guess) that natural ordering in PETSc leads to a
distribution of points such that all processors get the same number of
points ( [0, n/p) on proc 0, [n/p, 2n/p) on proc 1, ... ) unless n%p != 0,
in which case the first k (with k = n%p) processors receive 1 point extra.
Am I wrong to assume this?

Thanks,
Mohammad

PS: Is it relevant that the partitioning indexset is obtained via
ParMetis?partitiong
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