Hello Lucas, In your sequence of systems, is A changing? Are all right-hand sides available from the get-go? In that case, you can solve everything in a block fashion and that’s how you could get real improvements. Also, instead of PCCHOLESKY on A^T * A + KSPCG, you could use PCQR on A + KSPPREONLY, but this may not be needed, cf. Jed’s answer.
Thanks, Pierre > On 1 Mar 2022, at 12:54 AM, Lucas Banting <[email protected]> wrote: > > Hello, > > I have an MPIDENSE matrix of size about 200,000 x 200, using KSPLSQR on my > machine a solution takes about 15 s. I typically run with six to eight > processors. > I have to solve the system several times, typically 4-30, and was looking for > recommendations on reusable preconditioners to use with KSPLSQR to increase > speed. > > Would it make the most sense to use PCCHOLESKY on the smaller system A^T * A? > > Thanks, > Lucas
