Actual source code: degr.c

  1: #define PETSCMAT_DLL

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

 5:  #include petsc.h
 6:  #include src/mat/color/color.h

 10: PetscErrorCode MINPACKdegr(PetscInt *n,PetscInt * indrow,PetscInt * jpntr,PetscInt * indcol,PetscInt * ipntr,PetscInt * ndeg,PetscInt * iwa)
 11: {
 12:     /* System generated locals */
 13:     PetscInt i__1, i__2, i__3;

 15:     /* Local variables */
 16:     PetscInt jcol, ic, ip, jp, ir;

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

 58:     /* Parameter adjustments */
 59:     --iwa;
 60:     --ndeg;
 61:     --ipntr;
 62:     --indcol;
 63:     --jpntr;
 64:     --indrow;

 66:     /* Function Body */
 67:     i__1 = *n;
 68:     for (jp = 1; jp <= i__1; ++jp) {
 69:         ndeg[jp] = 0;
 70:         iwa[jp] = 0;
 71:     }

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

 77:     i__1 = *n;
 78:     for (jcol = 2; jcol <= i__1; ++jcol) {
 79:         iwa[jcol] = *n;

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

 84:         i__2 = jpntr[jcol + 1] - 1;
 85:         for (jp = jpntr[jcol]; jp <= i__2; ++jp) {
 86:             ir = indrow[jp];

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

 91:             i__3 = ipntr[ir + 1] - 1;
 92:             for (ip = ipntr[ir]; ip <= i__3; ++ip) {
 93:                 ic = indcol[ip];

 95: /*              Array iwa marks columns which have contributed to */
 96: /*              the degree count of column jcol. Update the degree */
 97: /*              counts of these columns as well as column jcol. */

 99:                 if (iwa[ic] < jcol) {
100:                     iwa[ic] = jcol;
101:                     ++ndeg[ic];
102:                     ++ndeg[jcol];
103:                 }
104:             }
105:         }
106:     }
107:     return(0);
108: }