Logistic function
When we are solving classifcation problem,we seldom use linear regression method.We should define a new function called logistic function to be our hypothesis.
and we should notice that
.
Decision Boundary
Decision boundary is a function of theta. It seperates the area of y=1 and y=0.
theta'*X can be a non-linear .
Cost Function
We have the cost function in the form that :
Gradient Decent
In order to minimize the cost function , we can use gradient decent ,and the same as linear regression problem , we should update theta simultaneously.
Library Function
We can use OCTAVE's library function to calculate the gradient decent like library function 'fminunc'.
Pay attention
(1) The hypothesis is not equal to theta*X' like linear regression
(2)
