Hi, As a part of implementing this process by ourself, we would like to eliminate boundary dofs. By reading DMStag code, we guess we can use DMStagStencilToIndexLocal MatZeroRowsLocal
We note that DMStagStencilToIndexLocal is not explicitly defined in the header file. Is this function ready to use? And will we be able to eliminate the dofs using the above functions? Thanks, Qi On Jul 16, 2021, at 8:17 PM, Barry Smith <[email protected]<mailto:[email protected]>> wrote: Zakariae, MatGetSubMatrix() was removed a long time ago, the routine is now MatCreateSubMatrix() but it does not work in way you had hoped. There is currently no mechanism to move values you put into the sub matrix back into the original larger matrix (though perhaps there should be?). Please look at MatCreateSubMatrixVirtual() and also MatCreateNest() to see if either of those approaches satisfy your needs. Please let us know if there are extensions that would be useful for you to accomplish what you need. Barry On Jul 16, 2021, at 7:45 PM, Jorti, Zakariae via petsc-users <[email protected]<mailto:[email protected]>> wrote: Hello, I have a matrix A = [A00 , A01 ; A10, A11]. I extract the submatrix A11 with MatGetSubMatrix. I only know the global IS is1 and is2, so to get A11 I call: MatGetSubMatrix(A,is2,is2,MAT_INITIAL_MATRIX,&A11); I want to modify A11 and update the changes on the global matrix A but I could not find any MatRestoreSubMatrix routine. Is there something similar to VecGetSubVector and VecRestoreSubVector for matrices that uses only global indices? Many thanks. Best regards, Zakariae
