[petsc-users] Question about TSSetIJacobian examples

[Torquil Macdonald Sørensen]

Sorry, I meant: what is the reason for MatAssemblyBegin/End being run
for matrix A, in the case when A != B?

Best regards,
Torquil Sørensen

On 25/01/16 11:58, Torquil Macdonald Sørensen wrote:
> Hi!
>
> I have been looking at some of the PETSc examples where TSSetIJacobian,
> and there is one thing which is unclear to me. Consider e.g. the example:
>
> http://www.mcs.anl.gov/petsc/petsc-current/src/ts/examples/tutorials/ex8.c.html
>
> In the function RoberJacobian(), CEJacobian(), OregoJacobian(), there
> are two matrix function arguments A and B. The matrix A is the one that
> is actually set in the code. My question is: what is the purpose of
>
> MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);
> MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);
>
> when A != B at the end of the function? How does that piece of code
> affect B? In the documentation of these functions it says that they are
> to be called after e.g. MatSetValues. But MatSetValues have not been
> called on B in those functions, so that's why I'm wondering what those
> lines are for.
>
> Best regards,
> Torquil Sørensen
>