[petsc-users] KSP has an extra iteration when use shell matrix

[Yi Hu]

Dear PETSc team,
 
I am still trying to sort out my previous thread https://lists.mcs.anl.gov/pipermail/petsc-users/2024-January/050079.html using a minimal working example. However, I encountered another problem. Basically I combined the basic usage of SNES solver and shell matrix and tried to make it work. The jacobian of my snes is replaced by a customized MATOP_MULT. The minimal example code can be viewed here https://github.com/hyharry/small_petsc_test/blob/master/test_shell_jac/ex1f.F90 
 
When running with -ksp_monitor -ksp_converged_reason, it shows an extra mymult step, and hence ruin my previous converged KSP result. Implement a customized converged call-back also does not help. I am wondering how to skip this extra ksp iteration. Could anyone help me on this?
 
Thanks for your help.
 
Best wishes,
Yi

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