Hello,

I'd like to write code that allows access to a block of a matrix for use as an lvalue or rvalue through a function call.

Something along the lines of

class BigVec {
public:
Vector4d vec;

Vector2d & LittleVec()
{
return vec.block<2,1>(0,0);
}

};

int main(int argc, char ** argv)
{
BigVec bv;

bv.LittleVec() = Vector2d::Ones();
cout << bv.LittleVec();
}

When compiling I get:
"invalid initialization of non-const reference of type ‘Eigen::Vector2d&’ from an rvalue of type Eigen::Block<Eigen::Matrix<double, 4, 1>, 2, 1, false, true>’"

A potentially related issue:
http://listengine.tuxfamily.org/lists.t ... 00145.html

It seems like the solution is in getting the return type of the function right, but I'm not sure what that would be.

Thanks,
Adam

have a look at Eigen/src/Geometry/Transform.h file to see such examples. Search for linear() and translation().

Thanks for the help!

By making the return type Block (not as a reference) the code works.

class BigVec {
public:
Vector4d vec;

Block<Vector4d, 2, 1> LittleVec()
{
return vec.block<2, 1>(0, 0);
}

};