code: def _cost_method(self, *args, **kwargs):
          
  
          cost_val = self.thresh * nuclear_norm(cube2matrix(args[0]))
  
          if 'verbose' in kwargs and kwargs['verbose']:
              print(' - NUCLEAR NORM (X):', cost_val)
  
          return cost_val
docs: Calculate low-rank component of the cost
  
          This method returns the nuclear norm error of the deconvolved data in
          matrix form
  
          Returns
          -------
          float low-rank cost component