[Machine Learning_Andrew Ng]--Sigmoid() Function.

$$g(z)=\frac{1}{1+e^{-z}}$$

In octave

function g = sigmoid(z)
%SIGMOID Compute sigmoid functoon
%   J = SIGMOID(z) computes the sigmoid of z.

% You need to return the following variables correctly 
g = zeros(size(z));

% ====================== YOUR CODE HERE ======================
% Instructions: Compute the sigmoid of each value of z (z can be a matrix,
%               vector or scalar).
g = 1 ./(1 + exp(-z))




% =============================================================

end