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use generator_iterator with random number generators

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[SVN r11741]
This commit is contained in:
Jens Maurer 2001-11-19 22:19:15 +00:00
parent 44f6a441f7
commit f5f555f811
1 changed files with 22 additions and 7 deletions
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29
random_demo.cpp
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@ -22,6 +22,7 @@
#include <boost/random/linear_congruential.hpp>
#include <boost/random/uniform_smallint.hpp>
#include <boost/random/uniform_01.hpp>
#include <boost/generator_iterator.hpp>
#ifdef BOOST_NO_STDC_NAMESPACE
namespace std {
@ -35,14 +36,15 @@ typedef boost::minstd_rand base_generator_type;
// This is a reproducible simulation experiment.
void experiment(base_generator_type & generator)
{
boost::uniform_smallint<base_generator_type> die(generator, 1, 6);
typedef boost::uniform_smallint<base_generator_type> generator_type;
generator_type die_gen(generator, 1, 6);
#if 0 // iterator interface removed
// you can use a STL Iterator interface
// For an STL iterator interface, use iterator_adaptors.hpp
boost::generator_iterator_generator<generator_type>::type
die = boost::make_generator_iterator(die_gen);
for(int i = 0; i < 10; i++)
std::cout << *die++ << " ";
std::cout << '\n';
#endif
}
int main()
@ -60,9 +62,22 @@ int main()
for(int i = 0; i < 10; i++)
std::cout << uni() << '\n';
// change seed to something else
// Make sure the seed is unsigned, otherwise the wrong overload may be
// selected with mt19937.
/*
* Change seed to something else
* Make sure the seed is unsigned, otherwise the wrong overload may be
* selected with mt19937.
*
* 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";