code: def derivative(self, x):
          
          if self.is_linear:
              return self
          else:
              return FunctionalLeftVectorMult(self.functional.derivative(x),
                                              self.vector)
docs: Return the derivative at ``x``.
  
          Left scalar multiplication and derivative are commutative:
  
              ``FunctionalLeftVectorMult(op, y).derivative(z) ==
              FunctionalLeftVectorMult(op.derivative(z), y)``
  
          Returns
          -------
          derivative : `FunctionalLeftVectorMult`