I have a strange behaviour in the example below:

the output is
4 5 6
7
5

it should be
4 5 6
5
5

doesn't it ?

The version of eigen I use is the 2.0



#include
#include

using namespace Eigen;
using namespace std;


int main()
{

Matrix3d C;
C << 1, 2, 3,
4, 5, 6,
7, 8, 9;
cout << C.row(1) << endl;
cout << C.row(1)[1] << endl;
Vector3d tmp = C.row(1);
cout << tmp[1] << endl;
}

OK, you found a bug, and it's really embarrassing that something of that order of magnitude stayed unnoticed until now. However it's not in the row expression, it's in the MatrixBase::operator[].

I modified your testcase as follows:

Code: Select all

#include
#include

using namespace Eigen;
using namespace std;


int main()
{

Matrix3d C;
C << 1, 2, 3,
4, 5, 6,
7, 8, 9;
cout << "C.row(1)[1]: " << C.row(1)[1] << endl;
cout << "C.row(1)(1): " << C.row(1)(1) << endl;
cout << "C.row(1).nestByValue()[1]: " << C.row(1).nestByValue()[1] << endl;
cout << "C.row(1).coeff(1): " << C.row(1).coeff(1) << endl;
Vector3d tmp = C.row(1);
cout << tmp[1] << endl;
}


And I get this output:

Code: Select all

C.row(1)[1]: 7
C.row(1)(1): 7
C.row(1).nestByValue()[1]: 5
C.row(1).coeff(1): 5
5


Inside the MatrixBase::operator[], the only potentially evil thing we do is derived() which is just a static_cast. Replacing that call by the static_cast makes no difference, so I am really puzzled. Gael to the rescue?

bug fixed,

the problem was in MapBase where the coeff(int) method was correct but not the coeffRef(int) one called by default by operator[int] and operator(int)

Hi,
don't be ashamed, it is very normal to find bugs, that is why you made the lib public, isn't it?
And by the way, you have the fastest response time I ever see.
Thanks for the support and again, for the lib, I really love it.


Manuel