On Mon, May 31, 2021 at 9:20 AM Michael Wick <[email protected]> wrote:
> Hi PETSc team: > > I am considering implementing a skew roller boundary condition for my > elasticity problem. The method is based on this journal paper: > http://inside.mines.edu/~vgriffit/pubs/All_J_Pubs/18.pdf > > Or you may find the method in the attached Bathe's slides, pages 9 -10. > > Roughly speaking, a (very) sparse matrix T will be created which takes the > shape [ I, O; O, R], where R is a 3x3 rotation matrix. And the original > linear problem K U = F will be modified into (T^t K T) (T^t U) = T^t F. In > doing so, one can enforce a roller boundary condition on a slanted surface. > > I think it can be an easy option if I can generate the T matrix and do two > matrix multiplications to get T^t K T. I noticed that there is a MatPtAP > function. Yet, after reading a previous discussion, it seems that this > function is not designed for this purposes ( > https://lists.mcs.anl.gov/pipermail/petsc-users/2018-June/035477.html). > Yes, and no. It is motivated and optimized for a Galerkin coarse grid operator for AMG solvers, but it is a projection and it should be fine. If not, we will fix it. We try to test our methods of "empty" operators , but I don't know if MatPtAP has ever been tested for super sparse P. Give it a shot and see what happens. Mark > > I assume I can only call MatMatMult & MatTransposeMatMult to do this job, > correct? Is there any existingly PETSc function to do T^t K T in one call? > > Thanks, > > Mike > >
