Hi everyone

I am doing a project using OpenCV and Eigen and in a specific part I have to do a concatenation of sparse matrices. I saw in the forum that this question has already been asked and some solutions have been proposed:

- The first one uses middleCols and middleRows to insert the new block but I cannot use this since I have to do vertical and horizontal concatenation in the same matrix.

- The other one get the concatenation using SparseMatrix<float>::InnerIterator, but it is slow and I need faster ways to do it.

P.D. If it helps, I should obtain at the end something like [SparseMatrix A, (zeros) ; (zeros), SparseMatrix B] given A and B.

Any suggestion? Thanks!

Currently the best is to do it by hand through a call to reserve(A.nonZeros()+B.nonZeros()) and a iterations over the non-zeros of A (and then B) and calls to insert(it.index()+offset_i,j+offset_j) = it.value() for the insertion. This will translate to fast "push-back".