1 #include <petsc/private/matimpl.h> /*I "petscmat.h" I*/ 2 3 /*@ 4 MatComputeBandwidth - Calculate the full bandwidth of the matrix, meaning the width 2k+1 where k diagonals on either side are sufficient to contain all the matrix nonzeros. 5 6 Collective 7 8 Input Parameters: 9 + A - The `Mat` 10 - fraction - An optional percentage of the Frobenius norm of the matrix that the bandwidth should enclose 11 12 Output Parameter: 13 . bw - The matrix bandwidth 14 15 Level: beginner 16 17 .seealso: `DMPlexCreate()`, `DMPlexSetConeSize()`, `DMPlexSetChart()` 18 @*/ 19 PetscErrorCode MatComputeBandwidth(Mat A, PetscReal fraction, PetscInt *bw) 20 { 21 PetscInt lbw[2] = {0, 0}, gbw[2]; 22 PetscInt rStart, rEnd, r; 23 24 PetscFunctionBegin; 25 PetscValidHeaderSpecific(A, MAT_CLASSID, 1); 26 PetscValidLogicalCollectiveReal(A, fraction, 2); 27 PetscAssertPointer(bw, 3); 28 PetscCheck(!(fraction > 0.0) || !(fraction < 1.0), PetscObjectComm((PetscObject)A), PETSC_ERR_SUP, "We do not yet support a fractional bandwidth"); 29 PetscCall(MatGetOwnershipRange(A, &rStart, &rEnd)); 30 for (r = rStart; r < rEnd; ++r) { 31 const PetscInt *cols; 32 PetscInt ncols; 33 34 PetscCall(MatGetRow(A, r, &ncols, &cols, NULL)); 35 if (ncols) { 36 lbw[0] = PetscMax(lbw[0], r - cols[0]); 37 lbw[1] = PetscMax(lbw[1], cols[ncols - 1] - r); 38 } 39 PetscCall(MatRestoreRow(A, r, &ncols, &cols, NULL)); 40 } 41 PetscCallMPI(MPIU_Allreduce(lbw, gbw, 2, MPIU_INT, MPI_MAX, PetscObjectComm((PetscObject)A))); 42 *bw = 2 * PetscMax(gbw[0], gbw[1]) + 1; 43 PetscFunctionReturn(PETSC_SUCCESS); 44 } 45