math_util.cc

题描述的是一个旅行商要到几个城市去

/* $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];
}


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;
}