code: def none(n, coef):
      
      return sp.sparse.csc_matrix(np.zeros((n, n)))
docs: Build a matrix of zeros for features that should go unpenalized
  
      Parameters
      ----------
      n : int
          number of splines
      coef : unused
          for compatibility with constraints
  
      Returns
      -------
      penalty matrix : sparse csc matrix of shape (n,n)