math_util.cc

来自「这是关于覆盖网的各种负载均衡算法的程序。好好研究」· CC 代码 · 共 54 行

/* $Id: math_util.cc,v 1.8 2005/08/02 19:35:49 jonathan Exp $
 * Jonathan Ledlie, Harvard University.
 * Copyright 2005.  All rights reserved.
 */

#include "error.h"
#include "math_util.h"

double poisson (double mean) {
  double u;
  while ((u = randPct()) == 0.);
  return (-mean) * log(u);
};

int poisson (int mean) {
  return (int)(poisson((double)mean));
}

double mean (vector<double> v) {
  double sum = 0.;
  for (int i = 0; i < v.size(); i++) {
    sum += v[i];
  }
  return sum/(double)v.size();
}

double square (double x) {
  return x*x;
}

double stddev (vector<double> v, double mean) {
  double sum = 0.;
  if (v.size() <= 1) return 0.;
  for (int i = 0; i < v.size(); i++) {
    sum += pow(v[i]-mean,2);
  }
  return sqrt (sum/(v.size()-1));
}

double randPct () {
  double ret = Rand ();
  ASSERT (ret >= 0. && ret < 1);
  return ret;
}

// Returns a number (a,b]
int unifRand (int a, int b) {
  ASSERT (a >= 0 && b >= 0);
  int diff = ABS ((a-b));
  int randValue = (int)(Rand()*(double)diff);
  return (int)(a + randValue);
}