
Ublas : 
Subject: Re: [ublas] vector/matrix_assign do not work for integral types (bug?)
From: Nasos Iliopoulos (nasos_i_at_[hidden])
Date: 20100817 08:05:59
Marco,
I missed that! It looks that it works great.
Best,
Nasos
> Date: Mon, 16 Aug 2010 23:06:30 +0200
> From: marco.guazzone_at_[hidden]
> To: ublas_at_[hidden]
> Subject: Re: [ublas] vector/matrix_assign do not work for integral types (bug?)
>
> Hi Nasos,
>
> On Mon, Aug 16, 2010 at 5:15 PM, Nasos Iliopoulos <nasos_i_at_[hidden]> wrote:
> > Marco,
> > indeed it seems that uBlas was designed without integral types in mind and I
> > think that some things can be tweaked to correct for this. Tweaking the
> > inequality should not affect anything important, as it only compares with
> > the epsilon.
> >
> > There is only one thing to consider, that in this case uBlas will be
> > comparing an integral type with a floating type, introducing an
> > inconsistency. I don't know if it is better to use mpl::is_integral to get
> > rid of this inconsistency (and hence complicate the code), or go with the
> > solution you propose. The way I see it though the <= will not create any
> > trouble so I vote going for it atm and just make a note for future
> > reference.
> >
>
> Maybe I miss something, but I don't see this problem.
> Let's analyze the "equals" and "expression_type_check" functions in
> "vector_assign.hpp" (similar considerations can be done for
> "matrix_assign.hpp"):
>  [code] 
> template<class E1, class E2, class S>
> BOOST_UBLAS_INLINE
> bool equals (const vector_expression<E1> &e1, const
> vector_expression<E2> &e2, S epsilon, S min_norm) {
> return norm_inf (e1  e2) <= epsilon *
> std::max<S> (std::max<S> (norm_inf (e1), norm_inf
> (e2)), min_norm);
> }
>
> template<class E1, class E2>
> BOOST_UBLAS_INLINE
> bool expression_type_check (const vector_expression<E1> &e1, const
> vector_expression<E2> &e2) {
> typedef typename type_traits<typename promote_traits<typename
> E1::value_type,
> typename
> E2::value_type>::promote_type>::real_type real_type;
> return equals (e1, e2, BOOST_UBLAS_TYPE_CHECK_EPSILON,
> BOOST_UBLAS_TYPE_CHECK_MIN);
> }
>  [/code] 
>
> Let e1 and e1 be two vector of ints (ublas::vector<int>)
> In "expression_type_check" we have:
> * E1::value_type ==> int
> * E2::value_type ==> int
> * real_type ==> int (type_traits<int>::real_type gives int)
> * BOOST_UBLAS_TYPE_CHECK_EPSILON
> ==> type_traits<real_type>::type_sqrt
> (std::numeric_limits<real_type>::epsilon ())
> ==> type_traits<int>::type_sqrt (std::numeric_limits<int>::epsilon ())
> ==> int
> * BOOST_UBLAS_TYPE_CHECK_MIN
> ==> type_traits<real_type>::type_sqrt (
> ::boost::is_integral<real_type>::value ? 0 :
> ((std::numeric_limits<real_type>::min) ()))
> ==> type_traits<int>::type_sqrt (
> ::boost::is_integral<int>::value ? 0 :
> ((std::numeric_limits<int>::min) ()))
> ==> int
>
> So when "equals" is called the inner check is done on integral
> expressions (note: in this case, norm_inf returns an int type too).
>
> Do you agree?
>
> I have prepared patch for:
> * detail/config.hpp
> * detail/vector_assign.hpp
> * detail/matrix_assign.hpp
>
> I didn't yet posted on TRAC cause of my previously posted patch on
> matrix_assign.hpp that waits to be applied (or refused). See:
> * http://lists.boost.org/MailArchives/ublas/2010/07/4420.php
> * https://svn.boost.org/trac/boost/ticket/4410
>
> What should I do?
> a) Post a patch for matrix_assign.hpp based on current ublas trunk
> (ignoring that patch)?
> b) Post a patch for matrix_assign.hpp, keeping into consideration that
> previously submitted patch?
>
> Best,
>
>  Marco
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