Re: [ublas] Return type of 'mean_square'

Subject: Re: [ublas] Return type of 'mean_square'
From: Nasos Iliopoulos (nasos_i_at_[hidden])
Date: 2015-08-18 12:02:11

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]> 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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