[petsc-users] KSPBuildResidual and KSPType compatibility

Fischer, Greg A. fischega at westinghouse.com
Mon Dec 6 10:19:51 CST 2021

Hello petsc-users,

I would like to check convergence against the infinity norm, so I defined my own convergence test routine with KSPSetConvergenceTest. (I understand that it may be computationally expensive.)

I would like to do this with the "ibcgs" method. When I use KSPBuildResidual and calculate the NORM_2 against the output vector, I get a value that differs from the 2-norm that gets passed into the convergence test function. However, when I switch to the "gcr" method, the value I calculate matches the function input value.

Is the KSPBuildResidual function only compatible with a subset of the KSPType methods? If I want to evaluate convergence against the infinity norm, do I need to set KSPSetInitialGuessNonzero and continually re-start the solver with a lower tolerance values until I get a satisfactory value of the infinity norm?



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