> On Sep 19, 2016, at 10:43 AM, Cyrill Vonplanta <cyrill.von.pla...@usi.ch> > wrote: > > Barry, > > Thanks a lot. I’d like to use this for a nonlinear variant of a > block-gauss-seidel smoother. I would like to use MatInvertBlockDiagonal for > speeding up my variant. > > I think I can work with this, however I also have the problem to turn my > initial matrix into one with a blocksize of 3.When I call: > > MatConvert(A, MATBAIJ, MAT_INITIAL_MATRIX, Dinverse);
MatConvert() creates a new matrix so you should not create the Dinverse beforehand; anything you put in Dinverse before is lost..m block size > 1 really only makes sense if the block size is really greater than one. So if A has blocks of size 3 you should create A as BAIJ and thus never need to call the convert routine. You can also set the block size for AIJ matrix to 3 and use MatInvertBlockDiagonal() on that matrix and not use the BAIJ matrix. Finally note that MatInvertBlockDiagonal() ends up calling (for block size 3) PetscKernel_A_gets_inverse_A_3() for each block. It sounds to me like that is what you would want for nonlinear variant of a block-gauss-seidel smoother.. Barry > > > Then the matrix Dinverse has blocksize 1 which comes from A. I checked the > blocksize before the conversion and it was 3, so it seems to get lost. > > What is the correct (and elegant) way to turn a matrix into a block matrix? > > > Best > Cyrill > > > > On 19/09/16 17:18, "Barry Smith" <bsm...@mcs.anl.gov> wrote: > >> >> Cyrill, >> >> This is very specialized for implementing point block Jacobi; I don't >> think it is something you would want to use directly. >> >> If you do want to use it, it simply returns the inverses of the block >> diagonals in column major form. You can then call MatSetValues() with with >> each of those blocks into another PETSc matrix. values[i*bs*bs] is the >> starting point of each block in the array. >> >> Barry >> >>> On Sep 19, 2016, at 4:55 AM, Cyrill Vonplanta <cyrill.von.pla...@usi.ch> >>> wrote: >>> >>> Dear PETSc-Users, >>> >>> I would like to use the inverted block diagonals of a a matrix. I have seen >>> the function MatInvertBlockDiagonal() but I don’t know how to create a >>> matrix out of them or an array of block matrizes. >>> >>> Does anyone have an example on how to use **values to create a PETSc >>> matrix? >>> >>> Thanks >>> Cyrill >>
