code: def calculate_l21_norm(X):
      """
      This function calculates the l21 norm of a matrix X, i.e., \sum ||X[i,:]||_2
  
      Input:
      -----
      X: {numpy array}, shape (n_samples, n_features)
  
      Output:
      ------
      l21_norm: {float}
      """
      return (np.sqrt(np.multiply(X, X).sum(1))).sum()
  
file_path: scikit-feature/skfeature/utility/sparse_learning.py
imports: import numpy
  from numpy import linalg
label_desc: Use image node_id 3 for calling a global function with example usage: calculate_l21_norm(X) and returns: np