Hands-On Machine Learning with C++

Eigen

Using the Eigen library, we can wrap a C++ array into the Eigen::Matrix object with the Eigen::Map type. The wrapped object will behave as a standard Eigen matrix. We have to parametrize the Eigen::Map type with the type of matrix that has the required behavior. Also, when we create the Eigen::Map object, it takes as arguments a pointer to the C++ array and matrix dimensions, as illustrated in the following code snippet:

std::vector<double> values;...auto x_data = Eigen::Map<Eigen::Matrix<double, Eigen::Dynamic,                         Eigen::Dynamic, Eigen::RowMajor>>(values.data(),                                                            rows_num,                                                            columns_num );