/* $Id: math_util.cc,v 1.3 2006-08-09 15:20:54 jonathan Exp $ * Jonathan Ledlie, Harvard University. * Copyright 2005.  All rights reserved. */#include <assert.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 percentile (vector<double> v, double percentile) {  //cout << "size " << v.size() << " pct " << percentile << endl;  if (v.size() == 0)     {    return 0;  }  if (v.size() == 1)   {    return v[0];  }  sort (v.begin(), v.end());  assert (percentile >= 0 && percentile <= 1);  int index = (int)(rint (percentile * v.size()));  //cout << "size " << v.size() << " pct " << percentile   //<< " index " << index << " v[i] " << v[index] << endl;  return v[index];}//返回0－1之間的隨機數(shù)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);}// Returns a list of numbers (a,b]vector<int> unifRands (int count, int a, int b){  vector<int> rands;  rands.reserve (count);  for (int i = 0; i < count; i++)  {    rands.push_back (unifRand (a, b));  }  return rands;}double log16 (double x){  const double logOf16 = log(16.);  return log(x)/logOf16;}double log8 (double x){  const double logOf8 = log(8.);  return log(x)/logOf8;}