[petsc-users] A matrix-free Jacobian for SNES using MatShell

[Jeremy Roberts]

Hi Barry,

Thanks for the quick response.

I have the unknown vector u globally accessible and so forgo use of the
user-defined context (I tried to get it to work---can it be used in
Fortran?).

I used

call SNESSetJacobian( snes, Jshell, Jshell, FOO, PETSC_NULL_OBJECT, ierr )

where FOO is an empty function having the correct argument types.  It seems
to work now, and I get the exact same answer using an explicit Jacobian
matrix and the shell version.  Is there a way to get around needing FOO at
all?

Jeremy
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