SD数学 : 勾配(grad)

定義

$ grad \ F = (\frac{\partial F}{\partial x}, \frac{\partial F}{\partial y})

$ \frac{\partial F(x, y)}{\partial x} = \lim_{\Delta x \rarr +0} \frac{F(x, y) - F(x - \Delta x, y)}{\Delta x}

$ \frac{\partial F(x, y)}{\partial y} = \lim_{\Delta y \rarr +0} \frac{F(x, y) - F(x, y - \Delta y)}{\Delta y}