Thank you all. These are the answers I was looking for! Best regards, Nicolas
2016-12-07 15:08 GMT+01:00 Mark Adams <[email protected]>: > Note, for best performance with ML and GAMG you want to give it the near > kernel for the 00 block. These are the 6 "rigid body modes" or zero energy > modes. PETSc provides some tools to do that (eg, > MatNullSpaceCreateRigidBody). > > On Wed, Dec 7, 2016 at 4:45 PM, Lawrence Mitchell < > [email protected]> wrote: > >> >> >> On 07/12/16 13:43, Karin&NiKo wrote: >> > Thanks Barry. >> > I must emphasize that my unknowns are not numbered in a regular way : >> > I am using a P2-P1 finite element and the middle nodes do not carry a >> > pressure DOF. So the global numbering is somewhat like : >> > ------------------------------------------------------------ >> ----------------------------------------------- >> > u1x, u1y, u1z, p, u2x, u2y, u2z, p2, u3x, u3y, u3z, u4x, u4y, u4z, p4, >> > ..... >> > node 1 DOF | node 2 DOF | node 3 DOF | node 4 DOF | >> > ------------------------------------------------------------ >> ----------------------------------------------- >> > >> > So my global matrix does not have a block-size of 4. Nevertheless the >> > A00 matrix has a block size of 3! >> > Is there a way to specify that only on the A00 sub-matrix? >> >> I presume you are defining the splits by providing ISes. You need to >> set the block size on the IS that defines the A00 block appropriately, >> then the submatrix will have it. >> >> Lawrence >> >> >
