Re: Return type of 'mean_square'

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 <[email protected]>:

> 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 <[email protected]>
>> 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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>>>
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