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 @*/
MatComputeBandwidth(Mat A,PetscReal fraction,PetscInt * bw)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