The formula in Equation 4.18 gives us a way to compute the effective degrees of freedom for a linear smoother given its hat matrix. Write functions knn_edf, local_reg_edf, and kernel_reg_edf that...

The formula in Equation 4.18 gives us a way to compute the effective degrees of freedom for a linear smoother given its hat matrix. Write functions knn_edf, local_reg_edf, and kernel_reg_edf that return the effective degrees of freedom given a training dataset X and the relevant tuning parameters