Re: [eigen] min(Arr1,Arr2) is it supposed to work?

[Gael Guennebaud <gael.guennebaud@xxxxxxxxx>]

oops, indeed the quick ref guide is again in advance with Eigen
development. Actually, it seems to be impossible for us to support
std::min(array1,array2) because std::min is implemented in a generic
way as:

    template<typename _Tp>  inline const _Tp&  min(const _Tp& __a,
const _Tp& __b)
    {
      if (__b < __a)
	return __b;
      return __a;
    }

therefore we cannot overload std::min for min(const
ArrayBase<T>&,const ArrayBase<T>&). To do so we would need overloads
for every expressions (Array<>, CwiseUnaryOp, CwiseBinaryOp, etc.).


I'm fixing the doc.

gael


On Fri, Apr 1, 2011 at 9:23 AM, Helmut Jarausch
<jarausch@xxxxxxxxxxxxxxxxxxx> wrote:
> Hi,
>
> is the following assumed to work (I saw it in the Quick Reference
> Guide)
>
> #include <Eigen/Core>
> #include <cmath>
> given
> Eigen::Array3f V1, V2, V3;
>  V1 << 1,2,3;
>  V2 << 2,1,5;
>  V3= V1.min(V2);       // this works
>  V3= std::pow(V1,2);   // this works, as well
>
>  V3= std::min(V1,V2);  // but this fails, see below
>  cout << V3 << endl;
> }
>
> Tmin.C:14:21:   instantiated from here
> /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.2/include/g++-v4/bits/
> stl_algobase.h:191:7: error: could not convert '((const
> Eigen::ArrayBase<Eigen::Array<float, 3, 1> >*)((const
> Eigen::Array<float, 3, 1>*)__b))->Eigen::ArrayBase<Derived>::operator<
> [with OtherDerived = Eigen::Array<float, 3, 1>, Derived =
> Eigen::Array<float, 3, 1>, typename Eigen::internal::traits<T>::Scalar
> = float](((const Eigen::ArrayBase<Eigen::Array<float, 3, 1> >&)((const
> Eigen::ArrayBase<Eigen::Array<float, 3, 1> >*)((const
> Eigen::Array<float, 3, 1>*)__a))))' to 'bool'
>
>
> Thanks for some info,
> Helmut.
>
>
>