Actual source code: degr.c

      1: /* degr.f -- translated by f2c (version of 25 March 1992  12:58:56). */

      3: #include <../src/mat/graphops/color/impls/minpack/color.h>

      5: PetscErrorCode MINPACKdegr(PetscInt *n, const PetscInt *indrow, const PetscInt *jpntr, const PetscInt *indcol, const PetscInt *ipntr, PetscInt *ndeg, PetscInt *iwa)
      6: {
      7:   /* System generated locals */
      8:   PetscInt i__1, i__2, i__3;

     10:   /* Local variables */
     11:   PetscInt jcol, ic, ip, jp, ir;

     13:   /*     subroutine degr */
     14:   /*     Given the sparsity pattern of an m by n matrix A, */
     15:   /*     this subroutine determines the degree sequence for */
     16:   /*     the intersection graph of the columns of A. */
     17:   /*     In graph-theory terminology, the intersection graph of */
     18:   /*     the columns of A is the loopless graph G with vertices */
     19:   /*     a(j), j = 1,2,...,n where a(j) is the j-th column of A */
     20:   /*     and with edge (a(i),a(j)) if and only if columns i and j */
     21:   /*     have a non-zero in the same row position. */
     22:   /*     Note that the value of m is not needed by degr and is */
     23:   /*     therefore not present in the subroutine statement. */
     24:   /*     The subroutine statement is */
     25:   /*       subroutine degr(n,indrow,jpntr,indcol,ipntr,ndeg,iwa) */
     26:   /*     where */
     27:   /*       n is a positive integer input variable set to the number */
     28:   /*         of columns of A. */
     29:   /*       indrow is an integer input array which contains the row */
     30:   /*         indices for the non-zeroes in the matrix A. */
     31:   /*       jpntr is an integer input array of length n + 1 which */
     32:   /*         specifies the locations of the row indices in indrow. */
     33:   /*         The row indices for column j are */
     34:   /*               indrow(k), k = jpntr(j),...,jpntr(j+1)-1. */
     35:   /*         Note that jpntr(n+1)-1 is then the number of non-zero */
     36:   /*         elements of the matrix A. */
     37:   /*       indcol is an integer input array which contains the */
     38:   /*         column indices for the non-zeroes in the matrix A. */
     39:   /*       ipntr is an integer input array of length m + 1 which */
     40:   /*         specifies the locations of the column indices in indcol. */
     41:   /*         The column indices for row i are */
     42:   /*               indcol(k), k = ipntr(i),...,ipntr(i+1)-1. */
     43:   /*         Note that ipntr(m+1)-1 is then the number of non-zero */
     44:   /*         elements of the matrix A. */
     45:   /*       ndeg is an integer output array of length n which */
     46:   /*         specifies the degree sequence. The degree of the */
     47:   /*         j-th column of A is ndeg(j). */
     48:   /*       iwa is an integer work array of length n. */
     49:   /*     Argonne National Laboratory. MINPACK Project. July 1983. */
     50:   /*     Thomas F. Coleman, Burton S. Garbow, Jorge J. More' */

     52:   PetscFunctionBegin;
     53:   /* Parameter adjustments */
     54:   --iwa;
     55:   --ndeg;
     56:   --ipntr;
     57:   --indcol;
     58:   --jpntr;
     59:   --indrow;

     61:   /* Function Body */
     62:   i__1 = *n;
     63:   for (jp = 1; jp <= i__1; ++jp) {
     64:     ndeg[jp] = 0;
     65:     iwa[jp]  = 0;
     66:   }

     68:   /*     Compute the degree sequence by determining the contributions */
     69:   /*     to the degrees from the current(jcol) column and further */
     70:   /*     columns which have not yet been considered. */

     72:   i__1 = *n;
     73:   for (jcol = 2; jcol <= i__1; ++jcol) {
     74:     iwa[jcol] = *n;

     76:     /*        Determine all positions (ir,jcol) which correspond */
     77:     /*        to non-zeroes in the matrix. */

     79:     i__2 = jpntr[jcol + 1] - 1;
     80:     for (jp = jpntr[jcol]; jp <= i__2; ++jp) {
     81:       ir = indrow[jp];

     83:       /*           For each row ir, determine all positions (ir,ic) */
     84:       /*           which correspond to non-zeroes in the matrix. */

     86:       i__3 = ipntr[ir + 1] - 1;
     87:       for (ip = ipntr[ir]; ip <= i__3; ++ip) {
     88:         ic = indcol[ip];

     90:         /*              Array iwa marks columns which have contributed to */
     91:         /*              the degree count of column jcol. Update the degree */
     92:         /*              counts of these columns as well as column jcol. */

     94:         if (iwa[ic] < jcol) {
     95:           iwa[ic] = jcol;
     96:           ++ndeg[ic];
     97:           ++ndeg[jcol];
     98:         }
     99:       }
    100:     }
    101:   }
    102:   PetscFunctionReturn(PETSC_SUCCESS);
    103: }