code: def derivative(self, point):
          
          return self.exponent * MultiplyOperator(point ** (self.exponent - 1),
                                                  domain=self.domain,
                                                  range=self.range)
docs: Derivative of this operator.
  
              ``PowerOperator(p).derivative(y)(x) == p * y ** (p - 1) * x``
  
          Parameters
          ----------
          point : `domain` element
              The point in which to take the derivative
  
          Returns
          -------
          derivative : `Operator`
              The derivative in ``point``
  
          Examples
          --------
          Use on vector spaces:
  
          >>> op = PowerOperator(odl.rn(3), exponent=2)
          >>> dop = op.derivative(op.domain.element([1, 2, 3]))
          >>> dop([1, 1, 1])
          rn(3).element([ 2.,  4.,  6.])
  
          Use with scalars:
  
          >>> op = PowerOperator(odl.RealNumbers(), exponent=2)
          >>> dop = op.derivative(2.0)
          >>> dop(2.0)
          8.0