1 #include <petsc/private/matimpl.h> /*I "petscmat.h" I*/
2
3 /*@C
4 MatCheckCompressedRow - Determines whether the compressed row matrix format should be used.
5 Compressed row format provides high performance routines by taking advantage of zero rows.
6
7 Collective
8
9 Input Parameters:
10 + A - the matrix
11 . nrows - number of rows with nonzero entries
12 . compressedrow - pointer to the struct Mat_CompressedRow
13 . ai - row pointer used by `MATSEQAIJ` and `MATSEQBAIJ`
14 . mbs - number of (block) rows represented by `ai`
15 - ratio - ratio of (num of zero rows)/m, used to determine if the compressed row format should be used
16
17 Level: developer
18
19 Note:
20 Supported types are `MATAIJ`, `MATBAIJ` and `MATSBAIJ`.
21
22 Developer Notes:
23 The reason this takes the `compressedrow`, `ai` and `mbs` arguments is because it is called by both the `MATSEQAIJ` and `MATSEQBAIJ` matrices and
24 the values are not therefore obtained by directly taking the values from the matrix object.
25 This is not a general public routine and hence is not listed in petscmat.h (it exposes a private data structure) but it is used
26 by some preconditioners and hence is labeled as `PETSC_EXTERN`
27
28 .seealso: `Mat`, `MATAIJ`, `MATBAIJ`, `MATSBAIJ.`
29 @*/
MatCheckCompressedRow(Mat A,PetscInt nrows,Mat_CompressedRow * compressedrow,PetscInt * ai,PetscInt mbs,PetscReal ratio)30 PETSC_EXTERN PetscErrorCode MatCheckCompressedRow(Mat A, PetscInt nrows, Mat_CompressedRow *compressedrow, PetscInt *ai, PetscInt mbs, PetscReal ratio)
31 {
32 PetscInt *cpi = NULL, *ridx = NULL, nz, i, row;
33
34 PetscFunctionBegin;
35 /* in case this is being reused, delete old space */
36 PetscCall(PetscFree2(compressedrow->i, compressedrow->rindex));
37
38 /* compute number of zero rows */
39 nrows = mbs - nrows;
40
41 /* if a large number of zero rows is found, use compressedrow data structure */
42 if (nrows < ratio * mbs) {
43 compressedrow->use = PETSC_FALSE;
44
45 PetscCall(PetscInfo(A, "Found the ratio (num_zerorows %" PetscInt_FMT ")/(num_localrows %" PetscInt_FMT ") < %g. Do not use CompressedRow routines.\n", nrows, mbs, (double)ratio));
46 } else {
47 compressedrow->use = PETSC_TRUE;
48
49 PetscCall(PetscInfo(A, "Found the ratio (num_zerorows %" PetscInt_FMT ")/(num_localrows %" PetscInt_FMT ") > %g. Use CompressedRow routines.\n", nrows, mbs, (double)ratio));
50
51 /* set compressed row format */
52 nrows = mbs - nrows; /* num of non-zero rows */
53 PetscCall(PetscMalloc2(nrows + 1, &cpi, nrows, &ridx));
54 row = 0;
55 cpi[0] = 0;
56 for (i = 0; i < mbs; i++) {
57 nz = ai[i + 1] - ai[i];
58 if (nz == 0) continue;
59 cpi[row + 1] = ai[i + 1]; /* compressed row pointer */
60 ridx[row++] = i; /* compressed row local index */
61 }
62 while (row < nrows) ridx[row++] = -1; // pad array
63 compressedrow->nrows = nrows;
64 compressedrow->i = cpi;
65 compressedrow->rindex = ridx;
66 }
67 PetscFunctionReturn(PETSC_SUCCESS);
68 }
69