[petsc-users] How can get the inverse matrix of P(transpose)AP

[Jed Brown]

Cong Li <solvercorleone at gmail.com> writes:

> Hi
>
> I met a problem when trying to get a inverse matrix.
>
> The problem is like this:
> I have a matrix P (m x k matrix, and k<<m) and a matrix A (m x m matrix,
> large SPD matrix). Now I want to get the inverse matrix of
> P(transpose)*A*p.

Can you back up and explain at a high level what you're trying to accomplish?

> Since P(transpose)*A*p is only a k x k matrix, and PETSc only supports
> sequential direct solver, I want to store P(transpose)*A*p in MATSEQDENSE
> type.
> And the questions are
> 1. given P and A are PETSc parallel matrix, for instance MATMPIAIJ, how can
> I get sequential dense matrix P(transpose)*A*p?
> 2. If I need to multiply P(transpose)*A*p with other parallel dense matrix,
> how I can do it?
>
> Thanks a lot.
>
> Cong
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