Re: [Boost-users] Newbie question: Random numbers.

From: Andrew Holden (aholden_at_[hidden])
Date: 2006-05-19 09:17:35

My first thought is that you probably shouldn't reinitialize the generator for every random number you need.  I would recommend that you create and seed "generator" once at the start of your program, then reuse it whenever you need a random number.

Perhaps something like the following:

namespace Random
{
        typedef boost::minstd_rand base_generator_type;
        typedef boost::uniform_int<> distribution_type;
        typedef boost::variate_generator<base_generator_type&, distribution_type> gen_type;
        
        //Declare the generator as a global variable for easy reuse
        base_generator_type generator(static_cast<unsigned long>(clock()));

        /***************************************************
         * initializes the random number generator         *
         **************************************************/
        void initialize()
        {
                for (int i = 0; i < 30000; ++i)
                        generator.seed(static_cast<unsigned long>(clock()));
        }

        /***************************************************
         * generates a random number between a and b       *
         * @param a the starting range                     *
         * @param b the integer ending range               *
         * @return N such that a <= N <= b                 *
         **************************************************/
        template <class T>
        T rand_int (const T& a, const T& b)
        {
                //Check the parameters
                BOOST_STATIC_ASSERT(boost::is_integral<T>::value);
                assert (b >= a);

                //Set up the desired distribution
                gen_type ran_gen(generator, distribution_type(a, b));

                //Get a random number
                return ran_gen();
        }
}

using Random::rand_int;

int main(int argc, char* argv[])
{
        Random::initialize();

        std::cout << rand_int (1,1000) << std::endl
                << rand_int (1,1000) << std::endl
                << rand_int (1,1000) << std::endl
                << rand_int (1,1000) << std::endl;

        return 0;
}
________________________________________
From: chun ping wang [mailto:cablepuff_at_[hidden]] 
Sent: Friday, May 19, 2006 3:55 AM
To: boost-users_at_[hidden]
Subject: [Boost-users] Newbie question: Random numbers.

I have a simple question, is there a very fast and effecient way to generate random numbers that are fast on the fly. The numbers are really randomize and distorted...

/***************************************************
 * generates a random number between a and b       *
 * @param a the starting range                     *
 * @param b the integer ending range               *
 * @return N such that a <= N <= b                 *
 **************************************************/
template <class T>
T randint(const T& a, const T& b)
{
  BOOST_STATIC_ASSERT(boost::is_integral<T>::value);
  assert (b >= a);
  typedef boost::minstd_rand base_generator_type;
  typedef boost::uniform_int<> distribution_type;
  typedef boost::variate_generator<base_generator_type&, distribution_type> gen_type;
  base_generator_type generator(boost::numeric_cast<unsigned long>(clock()));
  gen_type ran_gen(generator, distribution_type(a, b));
  for (int i = 0; i < 30000; ++i)
      generator.seed(boost::numeric_cast<unsigned long>(clock()));
  return ran_gen();
}

This works but is super slow... are there effective ways to do it... 

Thanks.