Eigen Library: Setting all Non-Zero elements in a SparseMatrix *Row* to Zero

Question

For a matrix A and row 'i' in MATLAB, I would do the following:

A(i,:) = zeros(size(A(i,:));

A stupid way to do the same would be to iterate through the whole row and setting the non-zero values to zero. This is not suitable as I am working with huge matrices (200,000+ columns) here.

Is there a simple and fast way to do this? I am using the SparseMatrix class in Eigen. I also know that there are at most 3 non zero values in each row. I don't know where.

I need this to edit a few rows in the matrix with new values. The idea is that I first make the whole row zero and then assign my values to certain elements on the same row.

The following question on StackOverflow was relevant but unfortunately had no answers.

Answer 1

The equivalent of the Matlab code above can be implemented using the setZero function, as follows:

A.row(i).setZero();

Note that this works for dense matrices, not sparse ones. The MatrixXd class is recommended if you want the size to be dynamic.