/*! @file relax_snode.c

 * \brief Identify initial relaxed supernodes

 *

 * 

 * -- SuperLU routine (version 2.0) --

 * Univ. of California Berkeley, Xerox Palo Alto Research Center,

 * and Lawrence Berkeley National Lab.

 * November 15, 1997

 *

 * Copyright (c) 1994 by Xerox Corporation.  All rights reserved.

 *

 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY

 * EXPRESSED OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.

 *

 * Permission is hereby granted to use or copy this program for any

 * purpose, provided the above notices are retained on all copies.

 * Permission to modify the code and to distribute modified code is

 * granted, provided the above notices are retained, and a notice that

 * the code was modified is included with the above copyright notice.

 * 

 */

#include "slu_ddefs.h"

/*! \brief

 *

 * 

 * Purpose

 * =======

 *    relax_snode() - Identify the initial relaxed supernodes, assuming that 

 *    the matrix has been reordered according to the postorder of the etree.

 * 

 */ 

void

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 */

	     )

{

    register int j, parent;

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

    ifill (relax_end, 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 = 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++;

	/* Search for a new leaf */

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

    }

    /*printf("No of relaxed snodes: %d; relaxed columns: %d\n", 

		nsuper, no_relaxed_col); */

}