[petsc-users] Argument out of range error only in certain mpi sizes

[Sajid Ali]

Hi PETSc developers,

I wanted to convert my code that in which I was using general Vec/Mat to
DMDA based grid management (nothing fancy just a 5-point complex stencil).
For this, I created a DA object and created the global solution vector
using this. This worked fine.

Now, I created the matrix using DMCreateMatrix and fill it using the
regular function. I get no error when I run the problem using mpirun -np 1
and I thought my matrix filling logic aligns with the DM non-zero locations
(Star Stencil, width 1). With mpirun -np 2, no errors either. But with
mpirun -np 4 or 8, I get errors which say : "Argument out of range/
Inserting a new nonzero at global row/column ... into matrix".

I would switch over the logic provided in KSP/ex46.c for filling the Matrix
via the MatSetStencil logic but I wanted to know what I was doing wrong in
my current code since I've never seen an error that depends on number of
mpi processes.

I'm attaching the code ( which works if the matrix is created without using
the DA, i.e. comment out line 159, uncomment 161/162 and I'm doing this on
a small grid to catch errors.).

Thanks in advance for the help.


-- 
Sajid Ali
Applied Physics
Northwestern University
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