[petsc-users] Solving singular system via direct solvers

[Ye Changqing]

Dear all,

I have a linear system constructed from discretizing a Neumann boundary value problem, and I want to solve it with a direct solver (to build up my own preconditioner). Usually, KSP returns a good solution without '-inf', while sometimes it fails. I referred to the corresponding chapter in the manual and found options '-pc_factor_shift_type' and '-pc_factor_shift_amount'. Could I use those options in my codes rather than runtime? Moreover, In my case, the program did not throw an error or warning due to '-inf' in the solution, I also wondered how to check the solution is 'good'?

Thanks,
Changqing
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