How to get the row address of an Eigen::Matrix

Question

I have an Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic> intensityEigenMat;

I would like to pass it row by row to a ceres cost function, so I would like to access the reference to its individual rows.

I tried using:

intensityEigenMat.row(0)

&intensityEigenMat.row(0)

&intensityEigenMat.row(0).data()

But none of these worked. What is the right syntax please?

Answer 1

First you need to check the storage order option, which can be ColMajor or RowMajor. Default is ColMajor, so you need a complex way to read the matrix row by row (including a stride factor)

If you are allowed to change the definition of your matrix to:

Eigen::Matrix<double, Eigen::Dynamic, Eigen::dynamic, Eigen::RowMajor > intensityEigenMat;

Then things will be easier, and you can use intensityEigenMat.row(i).data() or intensityEigenMat.data()+i*rowSize