Frank, We do not have support of MatMatMult() for BAIJ*BAIJ matrices. For BAIJ matrix, we only support BAIJ*DENSE. You may have to convert BAIJ to AIJ to use MatMatMult(). Hong ________________________________ From: petsc-users <[email protected]> on behalf of Frank Bramkamp <[email protected]> Sent: Wednesday, May 29, 2024 9:23 AM To: petsc-users <[email protected]> Subject: [petsc-users] Question on MatMatmult Dear PETSc Team, I would like to make a matrix-matrix product of two matrices. I try to use CALL MatMatMult(Mat_A,MAT_B,MAT_INITIAL_MATRIX,PETSC_DEFAULT_REAL,MAT_AB,IERROR). // calling from fortran When I try to use this function I get the ZjQcmQRYFpfptBannerStart This Message Is From an External Sender This message came from outside your organization. ZjQcmQRYFpfptBannerEnd Dear PETSc Team, I would like to make a matrix-matrix product of two matrices. I try to use CALL MatMatMult(Mat_A,MAT_B,MAT_INITIAL_MATRIX,PETSC_DEFAULT_REAL,MAT_AB,IERROR). // calling from fortran When I try to use this function I get the following error message: "Unspecified symbolic phase for product AB with A seqbaij, B seqbaij. The product is not supported” I am using the seqbaij matrix format. Is MatMatMult and MatProductSymbolic only defined for the standard point-wise matrix format but not for a blocked format ?! In the documentation, I could not see a hint on supported matrix formats or any limitations. The examples also just use a point-wise format (AIJ), as I can see so far. Greetings, Frank Bramkamp