Re: [eigen] bug in data() on col/row

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

Hi,

Matrices can be stored in either row-major or column-major order.
Eigen defaults to column-major and you were apparently expecting it to
be row-major, that's all :)

If you want row-major, do:

typedef Matrix<float,3,3,RowMajor> RowMajorMatrix3f;

and henceforth use this typedef instead of Matrix3f.

Cheers,
Benoit

2009/8/27 Benjamin Schindler <bschindler@xxxxxxxxxxx>:
> Hi
>
> I just discovered a nasty "bug" - depending on how you look at it -  in
> Eigen, see the following program:
>
> #include <eigen2/Eigen/Core>
>
> using namespace Eigen;
> using namespace std;
>
> void copy(const float *from, float *to)
> {
>    for(int i=0;i<3;i++)
>        to[i] = from[i];
> }
>
> int main(int argc, char** argv)
> {
>    Matrix3f m;
>    m << 1,2,3,4,5,6,7,8,9;
>    cout << m << endl << endl;
>    float var[3];
>    copy(m.row(0).data(), var);
>    Map<Vector3f> map(var);
>    cout << map.transpose() << endl;
> }
>
> bschindl@hundertwasser ~ $ ./test
> 1 2 3
> 4 5 6
> 7 8 9
>
> 1 4 7
>
> When I save m.row(0) in a Vector3f and output it, I of course get this:
>
>
> bschindl@hundertwasser ~ $ ./test
> 1 2 3
> 4 5 6
> 7 8 9
>
> 1 2 3
>
> That's a nasty thing - and can cause lots of pain...
> Is there something we can do about it?
>
> Cheers
> Benjamin
>
>
>
>
>