Getting error (numpy.ndarray not callable) in Finding derivative of Sigmoid function

Question

I am new to neutral network & was trying to find derivative of sigmoid function.please help me to fix this error. My code is like;

import numpy as np

def sigmoid_derivative(x):

a=1/np.exp(x) +1

s=1/a

ds=s(1-s) 

return ds  

x = np.array([1, 2, 3])

print ("sigmoid_derivative(x) = " + str(sigmoid_derivative(x)))

Output:Error, numpy.ndarray is not callable.

Answer 1

on line ds=s(1-s) you are calling numpy.ndarray s with parameter 1-s, I think you need ds=s * (1-s)

Answer 2

You're missing a multiplication operator:

ds= s * (1-s) 

Answer 3

First of all, you got the sigmoid function wrong.

What I suggest is something like:

def sigmoid(x):
    return 1.0 / (1.0 + np.exp(-x))


def sigmoid_derivative(x):
    return sigmoid(x) * (1 - sigmoid(x))

Here's a link that would help you understand better: Derivative of the Sigmoid function