On Wed, Jul 18, 2018 at 1:59 PM, Matthew Knepley <knep...@gmail.com> wrote:
> On Wed, Jul 18, 2018 at 1:31 PM David Knezevic <david.kneze...@akselos.com> > wrote: > >> I'm using SNES for a finite element contact solve, in which the sparsity >> pattern of the jacobian can change from one Newton iteration to the next >> (since the nodes on the contact surface move). >> >> In order to handle this I figured the best way would be to destroy the >> jacobian matrix and re-allocate it with a new sparsity pattern inside each >> call to FormJacobian, does that seem like a reasonable approach in this >> context? >> > > Yes. > > >> Also, I recall from an earlier discussion that this matrix re-allocation >> inside FormJacobian is supported by SNES, but I just wanted to confirm that? >> > > Yes. > > >> Also, I was wondering if there is any example where the matrix is >> re-allocated inside SNES iterations so that I can make sure that I do it >> correctly? >> > > No, unfortunately. Contributions always welcome :) > OK, as a test case I'd like to modify snes/tutorials/ex1.c to destroy and reallocate the jacobian matrix with the same sparsity pattern inside FormJacobian1 (once I can do that with the same sparsity pattern, then it should be straightforward to do the same thing with a modified sparsity pattern). To do that, I tried adding the following code inside FormJacobian1: ierr = MatDestroy(&B); ierr = MatCreate(PETSC_COMM_WORLD,&B);CHKERRQ(ierr); ierr = MatSetSizes(B,PETSC_DECIDE,PETSC_DECIDE,2,2);CHKERRQ(ierr); ierr = MatSetFromOptions(B);CHKERRQ(ierr); ierr = MatSetUp(B);CHKERRQ(ierr); That gives a segfault, so I gather something else is needed here, any suggestions on what I need to do? I guess I need to do something else in order to make sure that the SNES uses the newly created matrix (e.g. update the original Mat J)? Thanks, David
