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/*! @file qselect.c
* \brief Quickselect: returns the k-th (zero-based) largest value in A[].
*
* <pre>
* -- SuperLU routine (version 4.1) --
* Lawrence Berkeley National Laboratory.
* November, 2010
* </pre>
*/
#include "slu_ddefs.h"
double dqselect(int n, double A[], int k)
{
register int i, j, p;
register double val;
k = SUPERLU_MAX(k, 0);
k = SUPERLU_MIN(k, n - 1);
while (n > 1)
{
i = 0; j = n-1;
p = j; val = A[p];
while (i < j)
{
for (; A[i] >= val && i < p; i++);
if (A[i] < val) { A[p] = A[i]; p = i; }
for (; A[j] <= val && j > p; j--);
if (A[j] > val) { A[p] = A[j]; p = j; }
}
A[p] = val;
if (p == k) return val;
else if (p > k) n = p;
else
{
p++;
n -= p; A += p; k -= p;
}
}
return A[0];
}
float sqselect(int n, float A[], int k)
{
register int i, j, p;
register float val;
k = SUPERLU_MAX(k, 0);
k = SUPERLU_MIN(k, n - 1);
while (n > 1)
{
i = 0; j = n-1;
p = j; val = A[p];
while (i < j)
{
for (; A[i] >= val && i < p; i++);
if (A[i] < val) { A[p] = A[i]; p = i; }
for (; A[j] <= val && j > p; j--);
if (A[j] > val) { A[p] = A[j]; p = j; }
}
A[p] = val;
if (p == k) return val;
else if (p > k) n = p;
else
{
p++;
n -= p; A += p; k -= p;
}
}
return A[0];
}
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