Function MeanGrad

tensorflow/cc/gradients/math_grad.cc:742–766

REGISTER_GRADIENT_OP("Sum", SumGrad);

Status MeanGrad(const Scope& scope, const Operation& op,
                const std::vector<Output>& grad_inputs,
                std::vector<Output>* grad_outputs) {
  // The Mean gradient is just like the Sum gradient, except that
  // all gradients are also divided by the size of reduced groups.
  auto sum_grad = SumGradHelper(scope, op, grad_inputs);

  // The product of all entries in a tensor's shape is the total
  // number of entries in the tensor. This step calculates
  // n_input_entries/n_output_entries
  // = group_size
  auto input_shape = Shape(scope, op.input(0));
  auto output_shape = Shape(scope, op.output(0));
  auto zero = Const(scope, 0);
  auto group_size = SafeDivHelper(scope, Prod(scope, input_shape, zero),
                                  Prod(scope, output_shape, zero));

  // propagate sum_grad/group_size
  grad_outputs->push_back(
      Div(scope, sum_grad, Cast(scope, group_size, sum_grad.type())));

  // Stop propagation along reduction_indices
  grad_outputs->push_back(NoGradient());
  return scope.status();
}
REGISTER_GRADIENT_OP("Mean", MeanGrad);

Status ErfGrad(const Scope& scope, const Operation& op,