code: def add_bias(X):
    
  
    return numpy.hstack((numpy.ones((len(X),1), dtype=X.dtype), X))
docs: Helper function to add a bias column to the input array X
  
  
    Parameters:
  
      X (numpy.ndarray): The input data matrix. This must be a numpy.ndarray
        with 2 dimension wheres every row corresponds to one example of the data
        set, every column, one different feature.
  
  
    Returns:
  
      numpy.ndarray: The same input matrix X with an added (prefix) column of
        ones.