std::exponential_distribution
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<tbody> </tbody> template< class RealType = double > class exponential_distribution; |
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Produces random non-negative floating-point values x, distributed according to probability density function:
- P(x|) = e-x
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The value obtained is the time/distance until the next random event if random events occur at constant rate per unit of time/distance. For example, this distribution describes the time between the clicks of a Geiger counter or the distance between point mutations in a DNA strand.
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#include <iostream>
#include <iomanip>
#include <string>
#include <map>
#include <random>
int main()
{
std::random_device rd;
std::mt19937 gen(rd());
// if particles decay once per second on average,
// how much time, in seconds, until the next one?
std::exponential_distribution<> d(1);
std::map<int, int> hist;
for(int n=0; n<10000; ++n) {
++hist[2*d(gen)];
}
for(auto p : hist) {
std::cout << std::fixed << std::setprecision(1)
<< p.first/2.0 << '-' << (p.first+1)/2.0 <<
' ' << std::string(p.second/200, '*') << '\n';
}
:
0.0-0.5 *******************
0.5-1.0 ***********
1.0-1.5 *******
1.5-2.0 ****
2.0-2.5 **
2.5-3.0 *
3.0-3.5
3.5-4.0
Weisstein, Eric W. "Exponential Distribution." MathWorld - Wolfram Web.