Re: [Boost-users] [random] Singleton engine

Subject: Re: [Boost-users] [random] Singleton engine
From: Kevin Martin (kev82_at_[hidden])
Date: 2009-07-26 06:47:20

On 26 Jul 2009, at 03:44, Diederick C. Niehorster wrote:

> I have been writing a wrapper around the variate_generator as I always
> want to use the same number generator, but do want to use different
> distributions.

I must admit I haven't read all your code in detail, so it may do more  
than I realise, but I had the same problem as this a while ago. My  
solution was a little simpler, I just use a static boost::shared_ptr  
to hold the singleton instance and for a given distribution I put the  
variate_generator into a boost::function.

I like this approach because it will cause an exception if I try and  
use the generator before I've seeded it, and it will also complain if  
I accidently initialise it more than once.

Thanks,
Kevin Martin

static boost::shared_ptr<boost::mt19937> generator_;

boost::mt19937 &grng_generator() {
     if(generator_) return *generator_;
     throw std::runtime_error("Requrested RNG, but there isn't one");
}

void grng_setGenerator(boost::shared_ptr<boost::mt19937> ptr) {
     if(!ptr) throw std::runtime_error("Tried to set generator to NULL  
pointer");
     if(generator_) throw std::runtime_error("Tried to set generator  
more than once");
     generator_ = ptr;
}

template<class Distribution_>
boost::function0<typename Distribution_::result_type>  
grng_randomVariable(const Distribution_ &d) {
     boost::variate_generator<boost::mt19937&, Distribution_> rv(
      grng_generator(), d);
     return boost::function0<typename Distribution_::result_type>(rv);
}