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random_demo.cpp
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110 lines (92 loc) · 4.04 KB
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/* boost random_demo.cpp profane demo
*
* Copyright Jens Maurer 2000
* Distributed under the Boost Software License, Version 1.0. (See
* accompanying file LICENSE_1_0.txt or copy at
* http://www.boost.org/LICENSE_1_0.txt)
*
* $Id$
*
* A short demo program how to use the random number library.
*/
#include <iostream>
#include <fstream>
#include <ctime> // std::time
#include <boost/random/linear_congruential.hpp>
#include <boost/random/uniform_int.hpp>
#include <boost/random/uniform_real.hpp>
#include <boost/random/variate_generator.hpp>
#include <boost/generator_iterator.hpp>
// This is a typedef for a random number generator.
// Try boost::mt19937 or boost::ecuyer1988 instead of boost::minstd_rand
typedef boost::minstd_rand base_generator_type;
// This is a reproducible simulation experiment. See main().
void experiment(base_generator_type & generator)
{
// Define a uniform random number distribution of integer values between
// 1 and 6 inclusive.
typedef boost::uniform_int<> distribution_type;
typedef boost::variate_generator<base_generator_type&, distribution_type> gen_type;
gen_type die_gen(generator, distribution_type(1, 6));
// If you want to use an STL iterator interface, use iterator_adaptors.hpp.
boost::generator_iterator<gen_type> die(&die_gen);
for(int i = 0; i < 10; i++)
std::cout << *die++ << " ";
std::cout << '\n';
}
int main()
{
// Define a random number generator and initialize it with a reproducible
// seed.
base_generator_type generator(42);
std::cout << "10 samples of a uniform distribution in [0..1):\n";
// Define a uniform random number distribution which produces "double"
// values between 0 and 1 (0 inclusive, 1 exclusive).
boost::uniform_real<> uni_dist(0,1);
boost::variate_generator<base_generator_type&, boost::uniform_real<> > uni(generator, uni_dist);
std::cout.setf(std::ios::fixed);
// You can now retrieve random numbers from that distribution by means
// of a STL Generator interface, i.e. calling the generator as a zero-
// argument function.
for(int i = 0; i < 10; i++)
std::cout << uni() << '\n';
/*
* Change seed to something else.
*
* Caveat: std::time(0) is not a very good truly-random seed. When
* called in rapid succession, it could return the same values, and
* thus the same random number sequences could ensue. If not the same
* values are returned, the values differ only slightly in the
* lowest bits. A linear congruential generator with a small factor
* wrapped in a uniform_smallint (see experiment) will produce the same
* values for the first few iterations. This is because uniform_smallint
* takes only the highest bits of the generator, and the generator itself
* needs a few iterations to spread the initial entropy from the lowest bits
* to the whole state.
*/
generator.seed(static_cast<unsigned int>(std::time(0)));
std::cout << "\nexperiment: roll a die 10 times:\n";
// You can save a generator's state by copy construction.
base_generator_type saved_generator = generator;
// When calling other functions which take a generator or distribution
// as a parameter, make sure to always call by reference (or pointer).
// Calling by value invokes the copy constructor, which means that the
// sequence of random numbers at the caller is disconnected from the
// sequence at the callee.
experiment(generator);
std::cout << "redo the experiment to verify it:\n";
experiment(saved_generator);
// After that, both generators are equivalent
assert(generator == saved_generator);
// as a degenerate case, you can set min = max for uniform_int
boost::uniform_int<> degen_dist(4,4);
boost::variate_generator<base_generator_type&, boost::uniform_int<> > deg(generator, degen_dist);
std::cout << deg() << " " << deg() << " " << deg() << std::endl;
{
// You can save the generator state for future use. You can read the
// state back in at any later time using operator>>.
std::ofstream file("rng.saved", std::ofstream::trunc);
file << generator;
}
return 0;
}