Exponential

   Operand<TFloat32> input = tf.constant(
          new float[] {-3.0f,-1.0f, 0.0f,1.0f,3.0f});
   Exponential<TFloat32> exp = new Exponential<>(tf);
   Operand<TFloat32> result = exp.call(input);
   // result is [0.04978707f,  0.36787945f,  1.f,  2.7182817f, 20.085537f]