Re: [eigen] Allow Dynamic as template parameter in fixed-size Eigen methods

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

Hi!

This is similar to bug 579.
http://eigen.tuxfamily.org/bz/show_bug.cgi?id=579
It seems that segment, tail, and head were overseen in the fix.

Do you think, you can provide a patch handling these cases as well? 
(Basically, what you wrote below plus some additional doxygen docu, 
similar to https://bitbucket.org/eigen/eigen/commits/e1dfda4)

Cheers,
Christoph



On 13.12.2013 15:53, Márton Danóczy wrote:
> Hi all,
>
> currently, many Eigen methods have a dynamic-size and a fixed-size version,
> e.g.
>
>      VectorBlock<Derived> segment(Index start, Index size);
>      VectorBlock<Derived, Size> segment<int Size>(Index start);
>
> It would make generic programming a lot easier to add an overload
>
>      VectorBlock<Derived, Size> segment<int Size>(Index start, Index size);
>      {
>          EIGEN_STATIC_ASSERT_VECTOR_ONLY(Derived)
>          eigen_assert(Length == Dynamic || Length == length);
>          return  VectorBlock<Derived, Size>(derived(), start, size);
>      }
>
> The first two methods could then refer to this one:
>
>      VectorBlock<Derived> segment(Index start, Index size)
>      {
>          return segment<Dynamic>(start, size);
>      }
>
>      VectorBlock<Derived, Size> segment<int Size>(Index start)
>      {
>          EIGEN_STATIC_ASSERT(Size != Dynamic)
>          return segment<Size>(start, Size);
>      }
>
> This change would enable use cases such as the following (contrived)
> example:
>
>      template <int M>
>      struct Foo
>      {
>          Foo(Index m) : a(m*2) {}
>
>          void bar()
>          {
>              Index m = a.size() / 2;
>              a.segment<M>(0, m) += a.segment<M>(m, m);
>          }
>
>          enum { Rows = M == Dynamic ? Dynamic : M*2 };
>
>          Eigen::Array<float, Rows, 1> a;
>      };
>
> Marton


--
----------------------------------------------
Dipl.-Inf., Dipl.-Math. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
Enrique-Schmidt-Straße 5
28359 Bremen

Tel: +49 (421) 218-64252
----------------------------------------------