Re: template template par used for a container statistic

From:

Barry <dhb2000@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 05 Sep 2007 15:07:05 +0800

Message-ID:

<fblkiq$qlf$1@aioe.org>

er wrote:

hi,

a) what's wrong with this code? it looks like allocator is the
problem.

the commented version works fine, but if possible i'd rather not limit
myself to ublas::vector

b) the version that works is slow compared to mathematica. is there
anything i can do about it (datatype or algorithm)?

//code starts here
#include <numeric>
#include <stdexcept>
#include <boost/numeric/ublas/vector.hpp>

template<class T,template<typename E,typename A = std::allocator<E>
class C >

It seems that you angle parenthesis don't match

template
<
     class T,
     template <typname E, typename A = std::allocator<E> > class C
>

one more problem
can we reference E here for std::allocator<E>?
I think it's invalid.

As the code using template temlpate params I read,
they often ignore the name of the param like
template
<
     class T,
     template <class, class> class U
>

As the first time I tried to use this tech,
I wrote

template
<
     class T,
     template <class K> class U
>
class C
{
    typedef K the_type;
};

using K here is invalid.

      T mean(const C<T>& elems){
      //template<typename T>//works
      //T mean(const boost::numeric::ublas::vector<T>& elems){//works
              long int size = elems.size();
              if(size>0){
                      return accumulate(elems.begin(),elems.end(),0.0)/
size;
              }else{
                      throw std::runtime_error("Sample_stats::mean");
              };
      };
//main:
      boost_auxiliary::vector_double vec(10000000);
      iota(vec.begin(),vec.end(),0.0);
      std::cout<<"compute->"<<std::endl;
      double m =
Sample_stats::mean<double,boost::numeric::ublas::vector>(vec);

//code ends here

--
Thanks
Barry