Directional Derivative

• The rate at which the function changes in a certain direction
• The direction is inputted as $\hat{u}$
• Uses Gradient Operator

\text{D}_\hat{u} f(P_0) \\ = \lim_{h \to 0} \frac{f(P_h) - f(P_0)}{h} \\ = \hat{u} \cdot \vec{\nabla} f(P_0)