Concatenate sparse matrix Eigen

Question

I have two sparse matrices in Eigen, and I would like to join them vertically into one. As an example the target of the code would be:

SparseMatrix         


        

Answer 1

As far as I know, there is currently no built-in solution. You can be way more efficient than your solution by using the internal insertBack function:

SparseMatrix M(L.rows() + C.rows(), L.cols());
M.reserve(L.nonZeros() + C.nonZeros());
for(Index c=0; c::InnerIterator itL(L, c); itL; ++itL)
         M.insertBack(itL.row(), c) = itL.value();
    for(SparseMatrix::InnerIterator itC(C, c); itC; ++itC)
         M.insertBack(itC.row()+L.rows(), c) = itC.value();
}
M.finalize();