Re: [Boost-users] [fusion][mpl::math] generic math operations

From: Chris Weed (chrisweed_at_[hidden])
Date: 2007-01-22 08:20:43

Hi,
I wanted to try to write a DFT that can take a compile-time data
structure such as the following:

#include <boost/mpl/math/double.hpp>

// v = [1.01 2.01 3.01 4.01 5.01 6.01 7.01]
typedef boost::mpl::math::string_c_to_double<1,'.',0,1>::type D1;
typedef boost::mpl::math::string_c_to_double<2,'.',0,1>::type D2;
typedef boost::mpl::math::string_c_to_double<3,'.',0,1>::type D3;
typedef boost::mpl::math::string_c_to_double<4,'.',0,1>::type D4;
typedef boost::mpl::math::string_c_to_double<5,'.',0,1>::type D5;
typedef boost::mpl::math::string_c_to_double<6,'.',0,1>::type D6;
typedef boost::mpl::math::string_c_to_double<7,'.',0,1>::type D7;
typedef boost::mpl::math::string_c_to_double<8,'.',0,1>::type D8;

typedef boost::fusion::vector<D1,D2,D3,D4,D5,D6,D7,D8> VectorType;

and perform the fourier transform at compile time.

The DFT is fairly simple as a for-loop it would look like this:
std::vector<complex<float> >
fft(const std::vector<float>& v)
{
  std::vector<complex<float> > result(v.size(),complex<float>(0,0));
  complex<float> c(0,1);
  for(size_t i=0;i<v.size();++i)
    for(size_t j=0;j<v.size();++j)
    {
      result[i] += (v[i]*exp(-2*M_PI*c*i*j/v.size()));
    }
  return result;
}

To get this algorithm into fusion, I would need a function object for
times, divide, and exp.
Thanks,
Chris

On 1/22/07, Joel de Guzman <joel_at_[hidden]> wrote:
> Chris Weed wrote:
> > Hi,
> > I am interested in combining the fusion and mpl::math libraries, but I
> > am not sure if they currently support what I want to do.
> >
> > I want to use generic math operations that can easily switch between
> > run-time and compile-time. I think this would require writing the
> > mpl::math functions as "Polymorphic Function Object" as described in
> > the fusion documentation. I am not sure if there is any mpl::math
> > documentation that describes this.
> >
> > It looks like the MPL currently has some math operations that are
> > strictly meta-functions in boost/mpl/aux_/arithmetic_op.hpp. Are the
> > any plans to expand these to be functions also?
>
> It would be good to start with some use cases. With use cases,
> it's easier to understand what exactly you want to accomplish.
>
> Regards,
> --
> Joel de Guzman
> http://www.boost-consulting.com
> http://spirit.sf.net
>
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>