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

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

PetscErrorCode MINPACKslo(PetscInt *n, const PetscInt *indrow, const PetscInt *jpntr, const PetscInt *indcol, const PetscInt *ipntr, PetscInt *ndeg, PetscInt *list, PetscInt *maxclq, PetscInt *iwa1, PetscInt *iwa2, PetscInt *iwa3, PetscInt *iwa4)
{
  /* System generated locals */
  PetscInt i__1, i__2, i__3, i__4;

  /* Local variables */
  PetscInt jcol, ic, ip, jp, ir, mindeg, numdeg, numord;

  /*     Given the sparsity pattern of an m by n matrix A, this */
  /*     subroutine determines the smallest-last ordering of the */
  /*     columns of A. */
  /*     The smallest-last ordering is defined for the loopless */
  /*     graph G with vertices a(j), j = 1,2,...,n where a(j) is the */
  /*     j-th column of A and with edge (a(i),a(j)) if and only if */
  /*     columns i and j have a non-zero in the same row position. */
  /*     The smallest-last ordering is determined recursively by */
  /*     letting list(k), k = n,...,1 be a column with least degree */
  /*     in the subgraph spanned by the un-ordered columns. */
  /*     Note that the value of m is not needed by slo and is */
  /*     therefore not present in the subroutine statement. */
  /*     The subroutine statement is */
  /*       subroutine slo(n,indrow,jpntr,indcol,ipntr,ndeg,list, */
  /*                      maxclq,iwa1,iwa2,iwa3,iwa4) */
  /*     where */
  /*       n is a positive integer input variable set to the number */
  /*         of columns of A. */
  /*       indrow is an integer input array which contains the row */
  /*         indices for the non-zeroes in the matrix A. */
  /*       jpntr is an integer input array of length n + 1 which */
  /*         specifies the locations of the row indices in indrow. */
  /*         The row indices for column j are */
  /*               indrow(k), k = jpntr(j),...,jpntr(j+1)-1. */
  /*         Note that jpntr(n+1)-1 is then the number of non-zero */
  /*         elements of the matrix A. */
  /*       indcol is an integer input array which contains the */
  /*         column indices for the non-zeroes in the matrix A. */
  /*       ipntr is an integer input array of length m + 1 which */
  /*         specifies the locations of the column indices in indcol. */
  /*         The column indices for row i are */
  /*               indcol(k), k = ipntr(i),...,ipntr(i+1)-1. */
  /*         Note that ipntr(m+1)-1 is then the number of non-zero */
  /*         elements of the matrix A. */
  /*       ndeg is an integer input array of length n which specifies */
  /*         the degree sequence. The degree of the j-th column */
  /*         of A is ndeg(j). */
  /*       list is an integer output array of length n which specifies */
  /*         the smallest-last ordering of the columns of A. The j-th */
  /*         column in this order is list(j). */
  /*       maxclq is an integer output variable set to the size */
  /*         of the largest clique found during the ordering. */
  /*       iwa1,iwa2,iwa3, and iwa4 are integer work arrays of length n. */
  /*     Subprograms called */
  /*       FORTRAN-supplied ... min */
  /*     Argonne National Laboratory. MINPACK Project. August 1984. */
  /*     Thomas F. Coleman, Burton S. Garbow, Jorge J. More' */

  PetscFunctionBegin;
  /* Parameter adjustments */
  --iwa4;
  --iwa3;
  --iwa2;
  --list;
  --ndeg;
  --ipntr;
  --indcol;
  --jpntr;
  --indrow;

  /* Function Body */
  mindeg = *n;
  i__1   = *n;
  for (jp = 1; jp <= i__1; ++jp) {
    iwa1[jp - 1] = 0;
    iwa4[jp]     = *n;
    list[jp]     = ndeg[jp];
    /* Computing MIN */
    i__2   = mindeg;
    i__3   = ndeg[jp];
    mindeg = PetscMin(i__2, i__3);
  }

  /*     Create a doubly-linked list to access the degrees of the */
  /*     columns. The pointers for the linked list are as follows. */

  /*     Each un-ordered column ic is in a list (the degree list) */
  /*     of columns with the same degree. */

  /*     iwa1(numdeg) is the first column in the numdeg list */
  /*     unless iwa1(numdeg) = 0. In this case there are */
  /*     no columns in the numdeg list. */

  /*     iwa2(ic) is the column before ic in the degree list */
  /*     unless iwa2(ic) = 0. In this case ic is the first */
  /*     column in this degree list. */

  /*     iwa3(ic) is the column after ic in the degree list */
  /*     unless iwa3(ic) = 0. In this case ic is the last */
  /*     column in this degree list. */

  /*     If ic is an un-ordered column, then list(ic) is the */
  /*     degree of ic in the graph induced by the un-ordered */
  /*     columns. If jcol is an ordered column, then list(jcol) */
  /*     is the smallest-last order of column jcol. */

  i__1 = *n;
  for (jp = 1; jp <= i__1; ++jp) {
    numdeg   = ndeg[jp];
    iwa2[jp] = 0;
    iwa3[jp] = iwa1[numdeg];
    if (iwa1[numdeg] > 0) iwa2[iwa1[numdeg]] = jp;
    iwa1[numdeg] = jp;
  }
  *maxclq = 0;
  numord  = *n;

  /*     Beginning of iteration loop. */

L30:

  /*        Choose a column jcol of minimal degree mindeg. */

L40:
  jcol = iwa1[mindeg];
  if (jcol > 0) goto L50;
  ++mindeg;
  goto L40;
L50:
  list[jcol] = numord;

  /*        Mark the size of the largest clique */
  /*        found during the ordering. */

  if (mindeg + 1 == numord && !*maxclq) *maxclq = numord;

  /*        Termination test. */

  --numord;
  if (!numord) goto L80;

  /*        Delete column jcol from the mindeg list. */

  iwa1[mindeg] = iwa3[jcol];
  if (iwa3[jcol] > 0) iwa2[iwa3[jcol]] = 0;

  /*        Find all columns adjacent to column jcol. */

  iwa4[jcol] = 0;

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

  i__1 = jpntr[jcol + 1] - 1;
  for (jp = jpntr[jcol]; jp <= i__1; ++jp) {
    ir = indrow[jp];

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

    i__2 = ipntr[ir + 1] - 1;
    for (ip = ipntr[ir]; ip <= i__2; ++ip) {
      ic = indcol[ip];

      /*              Array iwa4 marks columns which are adjacent to */
      /*              column jcol. */

      if (iwa4[ic] > numord) {
        iwa4[ic] = numord;

        /*                 Update the pointers to the current degree lists. */

        numdeg = list[ic];
        --list[ic];
        /* Computing MIN */
        i__3   = mindeg;
        i__4   = list[ic];
        mindeg = PetscMin(i__3, i__4);

        /*                 Delete column ic from the numdeg list. */

        if (!iwa2[ic]) iwa1[numdeg] = iwa3[ic];
        else iwa3[iwa2[ic]] = iwa3[ic];

        if (iwa3[ic] > 0) iwa2[iwa3[ic]] = iwa2[ic];

        /*                 Add column ic to the numdeg-1 list. */

        iwa2[ic] = 0;
        iwa3[ic] = iwa1[numdeg - 1];
        if (iwa1[numdeg - 1] > 0) iwa2[iwa1[numdeg - 1]] = ic;
        iwa1[numdeg - 1] = ic;
      }
    }
  }

  /*        End of iteration loop. */

  goto L30;
L80:

  /*     Invert the array list. */

  i__1 = *n;
  for (jcol = 1; jcol <= i__1; ++jcol) iwa2[list[jcol]] = jcol;

  i__1 = *n;
  for (jp = 1; jp <= i__1; ++jp) list[jp] = iwa2[jp];
  PetscFunctionReturn(PETSC_SUCCESS);
}
