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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;
- }
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