Re: [eigen] Map with negative outer stride

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 02.02.2015 16:48, Chen-Pang He wrote:
> #define EIGEN_NO_DEBUG  // Disable eigen_assert
>
> #include <Eigen/Core>
> #include <iostream>
>
> int main()
> {
>      using namespace Eigen;
>
>      int data[] = { 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6 };
>
>      std::cout << Map<Matrix<int, 6, 6>, 0, OuterStride<-1> >(data + 5, 6, 6)
>                << std::endl;
> }

Too lazy to actually test it, but the following should work without 
disabling assertions:
Map<Matrix<int, 6, 6>, 0, OuterStride<1> >(data, 6, 6).rowwise().reverse()

This still requires a temporary vector with leading zeros. If you want 
to avoid that, I guess you need to write a small loop or write a 
CustomNullaryOp:
http://eigen.tuxfamily.org/dox-devel/classEigen_1_1DenseBase.html#a5b84f7ce5cc30b011683e3c2c6d816a8

Christoph



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Dipl.-Inf., Dipl.-Math. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
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