[petsc-users] Speed of KSPSolve using Matshell vs. regular matrix

[Yuyun Yang]

Hello team,

If I use KSPSolve for Ax=b using Matshell (a user-defined stencil equivalent of A) without preconditioning (since the standard PC would need information of the matrix so cannot apply it to matrix-free method), is it possible, or even inevitable to encounter significant slowdown compared to using a fully assembled matrix with a suitable preconditioner? I'm running a small example and it's already taking a long time for Matshell to converge.

Thanks for your help,
Yuyun
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