code: def nuclear_norm(data):
      r
  
      # Get SVD of the data.
      u, s, v = np.linalg.svd(data)
  
      # Return nuclear norm.
      return np.sum(s)
docs: r"""Nuclear norm
  
      This method computes the nuclear (or trace) norm of the input data.
  
      Parameters
      ----------
      data : np.ndarray
          Input data array
  
      Returns
      -------
      float nuclear norm value
  
      Examples
      --------
      >>> from modopt.math.matrix import nuclear_norm
      >>> a = np.arange(9).reshape(3, 3)
      >>> nuclear_norm(a)
      15.49193338482967
  
      Notes
      -----
      Implements the following equation:
  
      .. math::
          \|\mathbf{A}\|_* = \sum_{i=1}^{\min\{m,n\}} \sigma_i (\mathbf{A})