relax_snode.c~

SuperLU is a general purpose library for the direct solution of large, sparse, nonsymmetric systems

/*! @file relax_snode.c
 * \brief Identify initial relaxed supernodes
 *
 * <pre>
 * -- 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.
 * </pre>
 */

#include "slu_ddefs.h"
/*! \brief
 *
 * <pre>
 * Purpose
 * =======
 *    relax_snode() - Identify the initial relaxed supernodes, assuming that 
 *    the matrix has been reordered according to the postorder of the etree.
 * </pre>
 */ 
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); */
}