[petsc-users] matrix preallocation for unstructured finite element

[saturday luis]

Hi PETSc team:

Is there a way to make precise matrix preallocation for an unstructured
grid (I am not using the DMPlex object). Or do you have any example code
for estimating the dnz & onz data?

On top of my head, I can do a two-phase calculation. I can first give a
rough estimate and do one finite element assembly, then I will call
MatGetRow to locate the column indices for nonzero entries. Then in the
second step, I will destroy the Mat and create a new Mat with this obtained
sparsity pattern.

Do you have any suggestions?

Thanks!

Luis
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