Gradient checking

Approximating derivatives:

(Large triangle (+/- triangle))

$\frac{f(\Theta + \Epsilon) - f(\Theta - \Epsilon)}{2 \Epsilon} ~ g(\Theta)$

$f^'(\Theta) = \lim_{\Epsilon->0} \frac{f(\Theta + \Epsilon) - f(\Theta - \Epsilon)}{2 \Epsilon}$