GradientFunction* MatMulRegisterer(const ForwardOperation& op);
GradientFunction* SqrtRegisterer(const ForwardOperation& op);
GradientFunction* NegRegisterer(const ForwardOperation& op);
GradientFunction* SubRegisterer(const ForwardOperation& op);
GradientFunction* MulRegisterer(const ForwardOperation& op);
GradientFunction* Log1pRegisterer(const ForwardOperation& op);
GradientFunction* DivNoNanRegisterer(const ForwardOperation& op);

  return new SqrtGradientFunction(op.outputs[0]);
}

GradientFunction* NegRegisterer(const ForwardOperation& op) {
  return new NegGradientFunction;
}

GradientFunction* SubRegisterer(const ForwardOperation& op) {
  return new SubGradientFunction;
}

GradientFunction* MulRegisterer(const ForwardOperation& op) {
  return new MulGradientFunction(op.inputs);
}

        immediate_execution_ctx_.get(), 2.0f, &y_raw);
    ASSERT_EQ(errors::OK, status_.code()) << status_.message();
    y.reset(y_raw);
  }

  status_ = registry_.Register("Sub", SubRegisterer);
  ASSERT_EQ(errors::OK, status_.code()) << status_.message();

  ASSERT_NO_FATAL_FAILURE(CompareNumericalAndAutodiffGradients(
      SubModel, BuildGradModel(SubModel, registry_),