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: .  compressedrow - pointer to the struct Mat_CompressedRow
 17: .  ai            - row pointer used by seqaij and seqbaij
 18: .  mbs           - number of (block) rows represented by ai
 19: -  ratio         - ratio of (num of zero rows)/m, used to determine if the compressed row format should be used

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

 24:    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 
 25:                    the values are not therefore obtained by directly taking the values from the matrix object.
 26:    Level: developer
 27: @*/
 28: PetscErrorCode MatCheckCompressedRow(Mat A,Mat_CompressedRow *compressedrow,PetscInt *ai,PetscInt mbs,PetscReal ratio)
 29: {
 31:   PetscInt       nrows,*cpi=PETSC_NULL,*ridx=PETSC_NULL,nz,i,row;

 34:   if (!compressedrow->check) return(0);

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


 42:   /* compute number of zero rows */
 43:   nrows = 0;
 44:   for (i=0; i<mbs; i++){        /* for each row */
 45:     nz = ai[i+1] - ai[i];       /* number of nonzeros */
 46:     if (nz == 0) nrows++;
 47:   }

 49:   /* if a large number of zero rows is found, use compressedrow data structure */
 50:   if (nrows < ratio*mbs) {
 51:     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,ratio);
 53:   } else {
 54:     compressedrow->use = PETSC_TRUE;
 55:     PetscInfo3(A,"Found the ratio (num_zerorows %d)/(num_localrows %d) > %G. Use CompressedRow routines.\n",nrows,mbs,ratio);

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