[petsc-users] Fortran, KSPMonitorSet, and KSPMonitorTrueResidual

[Randall Mackie]

In previous versions of PETSc we use to be able to call KSPMonitorTrueResidual from within our custom KSPMonitor, using an approach that is now commented out in the example found at https://petsc.org/release/src/ksp/ksp/tutorials/ex2f.F90.html: ! 214: ! Cannot also use the default KSP monitor routine showing how it may be used from Fortran 215: ! since the Fortran compiler thinks the calling arguments are different in the two cases 216: ! 217: ! PetscCallA(PetscViewerAndFormatCreate(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_DEFAULT,vf,ierr)) 218: ! PetscCallA(KSPMonitorSet(ksp,KSPMonitorResidual,vf,PetscViewerAndFormatDestroy,ierr)) Instead, that example uses: 210: if (flg) then 211: vzero = 0 212: PetscCallA(KSPMonitorSet(ksp,MyKSPMonitor,vzero,PETSC_NULL_FUNCTION,ierr)) 213: ! Regardless of which of these approaches I try, I cannot use KSPMonitorTrueResidual in the MyKSPMonitor routine. I get the following error: [0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------[0]PETSC ERROR: Null argument, when expecting valid pointer[0]PETSC ERROR: Null Pointer: Parameter # 4[0]PETSC ERROR: See https://petsc.org/release/faq/ for trouble shooting.[0]PETSC ERROR: PETSc Release Version 3.23.3, May 30, 2025[0]PETSC ERROR: ./test with 2 MPI process(es) and PETSC_ARCH linux-gfortran-complex-debug on rmackie-VirtualBox-2024 by rmackie Mon Jun 23 11:34:04 2025[0]PETSC ERROR: Configure options: --with-clean=1 --with-scalar-type=complex --with-debugging=1 --with-fortran=1 --download-mpich=1[0]PETSC ERROR: #1 KSPMonitorTrueResidual() at /home/rmackie/PETSc/petsc-3.23.3/src/ksp/ksp/interface/iterativ.c:400[0]PETSC ERROR: #2 test.F90:303I attach a slightly modified version of the example that demonstrates this behavior.Thanks for the help,Randy

test.F90
Description: Binary data