Geografic-Information-System/lib/cdhc/watsonue.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "local_proto.h"


double *watson_u2_exp  (double *x, int n)
{
  double *xcopy, mean = 0.0, zbar = 0.0, fn2, fx, sum4 = 0.0;
  static double y[2];
  int i;

  if ((xcopy = (double *) malloc (n * sizeof (double))) == NULL)
  {
      fprintf (stderr, "Memory error in watson_u2_exp\n");
      exit (EXIT_FAILURE);
  }

  for (i = 0; i < n; ++i)
  {
    xcopy[i] = x[i];
    mean += x[i];
  }
  mean /= n;

  qsort (xcopy, n, sizeof (double), dcmp);

  for (i = 0; i < n; ++i)
  {
    fx = 1 - exp (-xcopy[i] / mean);
    if (fx <= 1e-5)
      fx = 1e-5;

    if (fx >= 0.99999)
      fx = 0.99999;

    /* sum3 += 2 * (i + 1) * (log (fx) + log (1.0 - fx[n - i - 1])); */
    fn2 = (2.0 * i + 1.0) / (2.0 * n);
    sum4 += (fx - fn2) * (fx - fn2);
    fn2 = (2.0 * (i + 1) - 1.0) / (2.0 * n);
    zbar += fx;
  }

  zbar /= n;
  y[0] = (1.0 / (n * 12) + sum4) - n * (zbar - .5) * (zbar - .5);
  y[0] *= 1.0 + 0.16 / n;

#ifdef NOISY
  fprintf (stdout,"  TEST19 WU2(E) =%10.4f\n", y[0]);
#endif				/* NOISY */

  free (xcopy);

  return y;
}