[petsc-users] question about MatSetLocalToGlobalMapping

[Karthikeyan Chockalingam - STFC UKRI]

Hello,

I created a new thread, thought would it be more appropriate (and is a continuation of my previous post). I want to construct the below K matrix (which is composed of submatrices)

K = [A P^T
       P   0]

Where K is of type MatMPIAIJ. I first constructed the top left [A] using MatSetValues().

Now, I would like to construct the bottom left [p] and top right [p^T] using MatSetValuesLocal().

To use  MatSetValuesLocal(),  I first have to create a local-to-global mapping using ISLocalToGlobalMappingCreate. I have created two mapping row_mapping and column_mapping.

Q1) At what point should I declare MatSetLocalToGlobalMapping – is it just before I use MatSetValuesLocal()?


I will use MatSetLocalToGlobalMapping(K, row_mapping, column_mapping) to build the bottom left [P].


Q2) Can now I reset the mapping as MatSetLocalToGlobalMapping(K, column_mapping, row_mapping) to build the top right [P^T]?


Many thanks!

Kind regards,
Karthik.









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