/*! @file ilu_relax_snode.c

 * \brief Identify initial relaxed supernodes

 *

 * 

 * -- SuperLU routine (version 4.0) --

 * Lawrence Berkeley National Laboratory

 * June 1, 2009

 * 

 */

#include "slu_ddefs.h"

/*! \brief

 *

 * 

 * Purpose

 * =======

 *    ilu_relax_snode() - Identify the initial relaxed supernodes, assuming

 *    that the matrix has been reordered according to the postorder of the

 *    etree.

 * 

 */

void

ilu_relax_snode (

	      const	int n,

	      int	*et,	       /* column elimination tree */

	      const int relax_columns, /* max no of columns allowed in a

					  relaxed snode */

	      int	*descendants,  /* no of descendants of each node

					 in the etree */

	      int	*relax_end,    /* last column in a supernode

					* if j-th column starts a relaxed

					* supernode, relax_end[j] represents

					* the last column of this supernode */

	      int	*relax_fsupc   /* first column in a supernode

					* relax_fsupc[j] represents the first

					* column of j-th supernode */

	     )

{

    register int j, f, parent;

    register int snode_start;	/* beginning of a snode */

    ifill (relax_end, n, EMPTY);

    ifill (relax_fsupc, n, EMPTY);

    for (j = 0; j < n; j++) descendants[j] = 0;

    /* Compute the number of descendants of each node in the etree */

    for (j = 0; j < n; j++) {

	parent = et[j];

	if ( parent != n )  /* not the dummy root */

	    descendants[parent] += descendants[j] + 1;

    }

    /* Identify the relaxed supernodes by postorder traversal of the etree. */

    for (j = f = 0; j < n; ) {

	parent = et[j];

	snode_start = j;

	while ( parent != n && descendants[parent] < relax_columns ) {

	    j = parent;

	    parent = et[j];

	}

	/* Found a supernode with j being the last column. */

	relax_end[snode_start] = j;		/* Last column is recorded */

	j++;

	relax_fsupc[f++] = snode_start;

	/* Search for a new leaf */

	while ( descendants[j] != 0 && j < n ) j++;

    }

}