Dear Pierre and Stefano, Yes - that is it! I had just stumbled onto that point as your email arrived thanks to Stefano's guidance, which suggested the problem was that the routine was receiving an integer when it was expecting something else... then a lightbulb finally switched on and I finally remembered that I needed to add the error variable as a final argument. I thought it was something silly on my part, and I wasn't mistaken there at least! Many thanks to both of you, best wishes, Dan. ________________________________ From: Pierre Seize <[email protected]> Sent: Friday, April 9, 2021 10:14 AM To: Stefano Zampini <[email protected]>; dazza simplythebest <[email protected]> Cc: [email protected] <[email protected]> Subject: Re: [petsc-users] Newbie question: Strange failure when calling PetscIntView from slepc application Hello, I think you forgot to pass ierr as the last argument of PetscIntView. Pierre On 09/04/21 11:52, Stefano Zampini wrote: ==841883== Invalid write of size 4 ==841883== at 0x503E784: petscintview_ (/data/work/slepc/PETSC/petsc-3.14.5/src/sys/error/ftn-custom/zerrf.c:109) ==841883== by 0x40262C: all_stab_routines_mp_write_rows_to_petsc_matrix_ (/data/work/rotplane/omega_to_zero/stability/test/tmp10/tmp3/tryme.F:17) ==841883== by 0x402465: MAIN__ (/data/work/rotplane/omega_to_zero/stability/test/tmp10/tmp3/tryme.F:40) ==841883== by 0x402221: main (in /data/work/rotplane/omega_to_zero/stability/test/tmp10/tmp3/trashy.exe) ==841883== Address 0x0 is not stack'd, malloc'd or (recently) free'd ==841883== This exactly points to the error and suggests you to take a look at /data/work/slepc/PETSC/petsc-3.14.5/src/sys/error/ftn-custom/zerrf.c, line 109 You are trying to write 4 bytes (most probably an int) where is not allowed. On Apr 9, 2021, at 12:32 PM, dazza simplythebest <[email protected]<mailto:[email protected]>> wrote: ==841883== Invalid write of size 4 ==841883== at 0x503E784: petscintview_ (/data/work/slepc/PETSC/petsc-3.14.5/src/sys/error/ftn-custom/zerrf.c:109) ==841883== by 0x40262C: all_stab_routines_mp_write_rows_to_petsc_matrix_ (/data/work/rotplane/omega_to_zero/stability/test/tmp10/tmp3/tryme.F:17) ==841883== by 0x402465: MAIN__ (/data/work/rotplane/omega_to_zero/stability/test/tmp10/tmp3/tryme.F:40) ==841883== by 0x402221: main (in /data/work/rotplane/omega_to_zero/stability/test/tmp10/tmp3/trashy.exe) ==841883== Address 0x0 is not stack'd, malloc'd or (recently) free'd ==841883==