[petsc-users] Problem about Residual evaluation

Yingjie Wu yjwu16 at gmail.com
Mon Apr 1 09:20:25 CDT 2019

Dear PETSc developers:

I've been using -snes_mf_operator and I've customized a precondition matrix
to solve my problem.I have two questions about the residuals of linear
steps(KSP residual).

1.Since I'm using a matrix-free method, how do we get KSP residuals in

r_m = b - A*x_m

Is finite difference used to approximate "A*x_m" ?

2.What is the difference between instruction ' -ksp_monitor ' and '
-ksp_monitor_true_residual ' in how they are calculated?


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