[petsc-users] Assembly of local Mat's to a parallel Mat

[Jed Brown]

Hui Zhang <mike.hui.zhang at hotmail.com> writes:

> Assembly it directly. I just found MatGetSubMatricesParallel.  

This is not a private implementation function so it's not a good place
to learn.  It also doesn't do what you want.

For your purpose, you can either loop over the entries of A_i inserting
them according to the R_i or you can create a block diagonal parallel
matrix A_i constructed by joining together all the diagonal blocks.
Presumably R is already parallel, so then you can use MatPtAP to
assemble the product.

Note that you might be able to assemble the block diagonal A directly.

> Maybe I can learn from the source codes of this function but I can not
> find where they are.

For navigating source code, see the manual section about setting up GNU
Global tags or etags.  PETSc functions are named to tab complete well
with tags.