Extracting the prolongation (transformation) matrix.

[nennigb]

Hello everyone,

I work on eigenvalue perturbation with periodic boundary conditions and I would like to know if it possible to explicitly get back the prolongation matrix $K$ (as defined in the README file) to export it as a petsc file. I dig a bit in python and cpp API, but I didn't find it.

Thanks a lot for your help,

Benoit

[jorgensd]

There is code to extract it on a single process in
a scipy sparse matrix at https://github.com/jorgensd/dolfinx_mpc/blob/main/python/dolfinx_mpc/utils/test.py#L89

[nennigb]

Thanks, I will have a look.

[nennigb]

It works thanks!

For parallel run, apart the bottleneck of collecting all constraints on the root node, is there another restriction ?

[jorgensd]

Well, since you collect the matrix on a single process, all future steps has to be done in serial, which reduces the performance significantly (and doing matrix-matrix-matrix multiplication is expensive).

[nennigb]

Thanks.