The sigmoidGradient function isn't defined

[Zijun-Peng]

I was writing the nnCostFunction function, but the sigmoidGradient function isn't defined?

NameError Traceback (most recent call last)
in
1 lambda_ = 0
2 J, _ = nnCostFunction(nn_params, input_layer_size, hidden_layer_size,
----> 3 num_labels, X, y, lambda_)
4 print('Cost at parameters (loaded from ex4weights): %.6f ' % J)
5 print('The cost should be about : 0.287629.')

in nnCostFunction(nn_params, input_layer_size, hidden_layer_size, num_labels, X, y, lambda_)
42
43 delta_3 = a3 - y_matrix
---> 44 delta_2 = delta_3.dot(Theta2)[:, 1:] * sigmoidGradient(a1.dot(Theta1.T))
45
46 Delta1 = delta_2.T.dot(a1)

NameError: name 'sigmoidGradient' is not defined

[Anim0011]

Its in utils.py file.