Demo of getting a dense vector from a row of a sparse matrix in Eigen

gistfile1.cpp

#include <iostream>
#include <vector>
#include <Eigen/Dense>
#include <Eigen/Sparse>

int main() {
    using namespace std;
    using namespace Eigen;

    vector<Triplet<double> > tripletList;
    tripletList.push_back(Triplet<double>(0, 0, 1.0));
    tripletList.push_back(Triplet<double>(0, 1, 0.0));
    tripletList.push_back(Triplet<double>(1, 0, 0.0));
    tripletList.push_back(Triplet<double>(1, 1, 1.0));

    SparseMatrix<double, RowMajor> m(2,2);
    m.setFromTriplets(tripletList.begin(), tripletList.end());
    VectorXd v = m.row(0);

    cout << "v=\n" << v << endl;

}