[petsc-users] Preconditioner for LSQR

[Pierre Jolivet]

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 <bantingl at myumanitoba.ca> 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

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