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First version of routine to do a quicksort type splitting without

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fully sorting the data. Used in Pilut. This version not debugged yet.
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cleary 2000-05-19 20:21:06 +00:00
parent 69f6927f3f
commit 156a59a9ec
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utilities/qsplit.c Normal file
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/*BHEADER**********************************************************************
* (c) 1998 The Regents of the University of California
*
* See the file COPYRIGHT_and_DISCLAIMER for a complete copyright
* notice, contact person, and disclaimer.
*
* $Revision$
*********************************************************************EHEADER*/
#include "utilities.h"
#include <math.h>
/*--------------------------------------------------------------------------
* hypre_DoubleQuickSplit
* C version of the routine "qsplit" from SPARSKIT
* Uses a quicksort-type algorithm to split data into
* highest "NumberCut" values without completely sorting them.
* Data is double precision data.
*--------------------------------------------------------------------------*/
int hypre_DoubleQuickSplit(double *values, int *indices,
int list_length, int NumberKept )
{
int ierr = 0;
double interchange_value;
double abskey;
int interchange_index;
int first, last;
int mid, j;
int done;
first = 0;
last = list_length-1;
if ( (NumberKept < first+1) || (NumberKept > last+1) )
return( ierr );
/* Loop until the "midpoint" is NumberKept */
done = 0;
for ( ; !done; )
{
mid = first;
abskey = fabs( values[ mid ]);
for( j = first+1; j <= last; j ++)
{
if( fabs( values[ j ]) > abskey )
{
mid ++;
/* interchange values */
interchange_value = values[ mid];
interchange_index = indices[ mid];
values[ mid] = values[ j];
indices[ mid] = indices[ j];
values[ j] = interchange_value;
indices[ j] = interchange_index;
}
}
/* interchange the first and mid value */
interchange_value = values[ mid];
interchange_index = indices[ mid];
values[ mid] = values[ first];
indices[ mid] = indices[ first];
values[ first] = interchange_value;
indices[ first] = interchange_index;
if ( mid+1 == NumberKept )
{
done = 1;
break;
}
if ( mid+1 > NumberKept )
last = mid - 1;
else
first = mid + 1;
}
return ( ierr );
}