Eigen: Flat view of Matrix in Templated Function

Question

For 1D resizing, the Eigen documentation suggests I use the following method to resize an array:

using Eigen;

MatrixXf X(2,2) << 1,2,3,4;
Map<RowVectorXf> v1(X.data(), X.size());

Except I have a templated vector, and can't use RowVectorXf

using Eigen;
template<class num>
void my_func(){

  Matrix<num,Dynamic,Dynamic> X(2,2) << 1,2,3,4;

  Map<Matrix<num,Dynamic,Dynamic>> unraveled(X.data(),X.size());
}

The example above fails with the following message:

error: static assertion faild: YOU_TRIED_CALLING_A_VECTOR_METHOD_ON_A_MATRIX

How do I obtain a flat view of an eigen matrix in a templated function?

Answer 1

The issue is that the Map is 2D and not 1D as you really want:

Map<Matrix<num,Dynamic,1>> unraveled(X.data(),X.size());

Then now it's a vector operation on your original X matrix.