The following code concatenates a vector of ones to a matrix:

Code: Select all

  using Eigen::VectorXd;
  using Eigen::MatrixXd;

MatrixXd cbind1(const Eigen::Ref<const MatrixXd> X) {
  const unsigned int n = X.rows();
  MatrixXd Y(n, 1 + X.cols());
  Y << VectorXd::Ones(n), X;
  return Y;
}


The function copies the contents of X to Y. How do I define the function so that it avoids doing the copy and returns a reference to a matrix containing VectorXd::Ones(n), X?

Thanks.

duplicate: http://stackoverflow.com/questions/4068 ... -reference