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

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


double *dmax  (double *x, int n)
{
  static double y[2];
  double *xcopy, sqrt2, sqrtn, mean = 0.0, sdx = 0.0, fx;
  double dp, dp_max, dm, dm_max;
  int i;

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

  sqrt2 = sqrt ((double) 2.0);
  sqrtn = sqrt ((double) n);

  for (i = 0; i < n; ++i)
  {
    xcopy[i] = x[i];
    mean += x[i];
    sdx += x[i] * x[i];
  }
  sdx = sqrt ((n * sdx - mean * mean) / (n * (n - 1.0)));
  mean /= n;

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

  for (i = 0; i < n; ++i)
  {
    xcopy[i] = (xcopy[i] - mean) / sdx;
    fx = 0.5 + normp (xcopy[i] / sqrt2) / 2.0;
    if (fx <= 1e-5)
      fx = 1e-5;

    if (fx >= 0.99999)
      fx = 0.99999;

    dp = (double) (i + 1) / (double) n - fx;
    dm = fx - i / (double) n;
    if (i == 0 || dp > dp_max)
      dp_max = dp;

    if (i == 0 || dm > dm_max)
      dm_max = dm;
  }

  y[0] = dp_max;
  y[1] = dm_max;

  free (xcopy);

  return y;
}