Cost Function

Linear regression: solve a minimisation problem

minimise $\theta_0, \theta_1$ for $J(\theta_0, \theta_1)$

cost function: $J(\theta_0, \theta_1) = \dfrac {1}{2m} \displaystyle \sum _{i=1}^m \left (h_\theta (x_{i}) - y_{i} \right)^2$