Re: [ublas] Return type of 'mean_square'

Subject: Re: [ublas] Return type of 'mean_square'
From: Nasos Iliopoulos (nasos_i_at_[hidden])
Date: 2015-09-16 20:53:12

I am not sure which part you are referring to but I believe it should 
should be something along those lines:

typedef ublas::promote_traits<typename M1::value_type, typename 
M1::value_type>::promote_type intermediate_t;

typedef boost::mpl::if_c<boost::mpl::is_integral<intermediate_t>::value,
                              long double,
                              intermediate_t>::type type;

-Nasos

On 09/16/2015 08:08 AM, Joaquim Duran Comas wrote:
> Currently, I've implemented:
>
> template <class AE>
> struct distance {
>     typedef boost::mpl::if_c<boost::mpl::is_integral<typename 
> AE::value_type>::value,
>                              long double,
>                              typename AE::value_type>::type type;
> };
>
> template <class AE>
> typename distance<AE>::type mean_square(const 
> boost::numeric::ublas::matrix_expression<AE> &me) {
>     typename distance<AE>::type s(0);
>
>     [...]
>
>     return s / (me().size1() * me().size2());
> }
>
> However, to use 'distance' struct in compare_distance functions, I 
> need the AE type, however in compare_distance function there are M1 
> and M2 matrices but not AE. Which expression I could use to get AE?
>
> Joaquim Duran
>
>
> 2015-08-18 18:02 GMT+02:00 Nasos Iliopoulos <nasos_i_at_[hidden] 
> <mailto:nasos_i_at_[hidden]>>:
>
>     Rethinking it it seems that if it is an integral type we should be
>     using floating type (like long double) and if not we should be
>     using the type itself. This would cover cases of using higher
>     precision arithmetic (like using boost::multi-precision)
>
>     Something like:
>
>     #include <boost/mpl/if.hpp>
>     #include <boost/type_traits/is_integral.hpp>
>     ...
>     typedef boost::mpl::if_c<boost::mpl::is_integral<typename
>     AE::value_type>::value, long double,  typename
>     AE::value_type>::type return_type;
>
>     -Nasos
>
>
>     On 08/18/2015 11:14 AM, Marco Guazzone wrote:
>
>         Don't know enough detail about the mean_square function, but
>         what if
>         AE::value_type is a long double?
>
>         Maybe you could use type deduction like the following:
>
>             typename ublas::promote_traits<typename
>         AE::value_type,double>::promote_type
>
>         I've written the following example:
>
>         --- [snip] ---
>         #include <boost/numeric/ublas/traits.hpp>
>         #include <iostream>
>
>         void foo(long double x)
>         {
>              (void)x;
>              std::cout << "LONG DOUBLE" << std::endl;
>         }
>         void foo(double x)
>         {
>              (void)x;
>              std::cout << "DOUBLE" << std::endl;
>         }
>
>         int main()
>         {
>              namespace ublas = boost::numeric::ublas;
>
>              std::cout << "long double vs. double -> ";
>              ublas::promote_traits<long double,double>::promote_type
>         ld_d = 0;
>              foo(ld_d);
>              std::cout << std::endl;
>
>              std::cout << "int vs. double -> ";
>          ublas::promote_traits<int,double>::promote_type i_d = 0;
>              foo(i_d);
>              std::cout << std::endl;
>
>              std::cout << "long vs. double -> ";
>          ublas::promote_traits<long,double>::promote_type l_d = 0;
>              foo(l_d);
>              std::cout << std::endl;
>         }
>         --- [/snip] ---
>
>         I've compiled on my machine (Linux 64bit with GCC 5.1.1
>         20150618 (Red
>         Hat 5.1.1-4)) with flags "-Wall -Wextra -ansi -pedantic", and the
>         result is:
>
>         long double vs. double -> LONG DOUBLE
>
>         int vs. double -> DOUBLE
>
>         long vs. double -> DOUBLE
>
>
>         Marco
>
>         On Tue, Aug 18, 2015 at 4:35 PM, Nasos Iliopoulos
>         <nasos_i_at_[hidden] <mailto:nasos_i_at_[hidden]>> wrote:
>
>             I was debating this myself. I think converting to double
>             is a good idea.
>
>             -Nasos
>
>             you cast the type do double before.
>
>
>             On 08/10/2015 11:40 AM, Joaquim Duran Comas wrote:
>
>             Hello,
>
>             Few days ago, I patched the function 'mean_square' for
>             vectors and matrices.
>             Currently, the current return type of the function is
>             AE::value_type. To get
>             better accuracy, is it better return double type than
>             AE::value_type
>             (specially if it is an integuer)?
>
>             Joaquim Duran
>
>
>
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