Date: 2015-10-02T22:12:14+00:00

Actual source code: compressedrow.c
petsc-3.6.2 2015-10-02
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      2: #include <petsc/private/matimpl.h>  /*I   "petscmat.h"  I*/

      6: /*@C
      7:    MatCheckCompressedRow - Determines whether the compressed row matrix format should be used.
      8:       If the format is to be used, this routine creates Mat_CompressedRow struct.
      9:       Compressed row format provides high performance routines by taking advantage of zero rows.
     10:       Supported types are MATAIJ, MATBAIJ and MATSBAIJ.

     12:    Collective

     14:    Input Parameters:
     15: +  A             - the matrix
     16: .  nrows         - number of rows with nonzero entries
     17: .  compressedrow - pointer to the struct Mat_CompressedRow
     18: .  ai            - row pointer used by seqaij and seqbaij
     19: .  mbs           - number of (block) rows represented by ai
     20: -  ratio         - ratio of (num of zero rows)/m, used to determine if the compressed row format should be used

     22:    Notes: By default PETSc will not check for compressed rows on sequential matrices. Call MatSetOption(Mat,MAT_CHECK_COMPRESSED_ROW,PETSC_TRUE); before
     23:           MatAssemblyBegin() to have it check.

     25:    Developer Note: The reason this takes the compressedrow, ai and mbs arguments is because it is called by both the SeqAIJ and SEQBAIJ matrices and
     26:                    the values are not therefore obtained by directly taking the values from the matrix object.
     27:                    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
     28:                    by some preconditioners and hence is labeled as PETSC_EXTERN

     30:    Level: developer
     31: @*/
     32: PETSC_EXTERN PetscErrorCode MatCheckCompressedRow(Mat A,PetscInt nrows,Mat_CompressedRow *compressedrow,PetscInt *ai,PetscInt mbs,PetscReal ratio)
     33: {
     35:   PetscInt       *cpi=NULL,*ridx=NULL,nz,i,row;

     38:   /* in case this is being reused, delete old space */
     39:   PetscFree2(compressedrow->i,compressedrow->rindex);

     41:   compressedrow->i      = NULL;
     42:   compressedrow->rindex = NULL;

     45:   /* compute number of zero rows */
     46:   nrows = mbs - nrows;

     48:   /* if a large number of zero rows is found, use compressedrow data structure */
     49:   if (nrows < ratio*mbs) {
     50:     compressedrow->use = PETSC_FALSE;

     52:     PetscInfo3(A,"Found the ratio (num_zerorows %d)/(num_localrows %d) < %g. Do not use CompressedRow routines.\n",nrows,mbs,(double)ratio);
     53:   } else {
     54:     compressedrow->use = PETSC_TRUE;

     56:     PetscInfo3(A,"Found the ratio (num_zerorows %d)/(num_localrows %d) > %g. Use CompressedRow routines.\n",nrows,mbs,(double)ratio);

     58:     /* set compressed row format */
     59:     nrows  = mbs - nrows; /* num of non-zero rows */
     60:     PetscMalloc2(nrows+1,&cpi,nrows,&ridx);
     61:     row    = 0;
     62:     cpi[0] = 0;
     63:     for (i=0; i<mbs; i++) {
     64:       nz = ai[i+1] - ai[i];
     65:       if (nz == 0) continue;
     66:       cpi[row+1]  = ai[i+1];    /* compressed row pointer */
     67:       ridx[row++] = i;          /* compressed row local index */
     68:     }
     69:     compressedrow->nrows  = nrows;
     70:     compressedrow->i      = cpi;
     71:     compressedrow->rindex = ridx;
     72:   }
     73:   return(0);
     74: }