2.19 偏微分作用素

	$\displaystyle \frac{\partial}{\partial x}f= \frac{\partial f}{\partial x}$
	$\displaystyle \left(\frac{\partial}{\partial x}\right)^2f= \frac{\partial}{\par... ...al}{\partial x}\frac{\partial f}{\partial x}= \frac{\partial^2 f}{\partial x^2}$
	$\displaystyle \left( \alpha\frac{\partial}{\partial x}+ \beta\frac{\partial}{\p... ...l y}f = \alpha\frac{\partial f}{\partial x}+ \beta\frac{\partial f}{\partial y}$
	$\displaystyle \frac{\partial}{\partial x}g\frac{\partial}{\partial x}f= \frac{\... ...g}{\partial x}\frac{\partial f}{\partial x}+ g\frac{\partial^2 f}{\partial x^2}$

	$\displaystyle \frac{\partial}{\partial x}\frac{\partial}{\partial x} = \left(\frac{\partial}{\partial x}\right)^2= \frac{\partial^2}{\partial x^2}$
	$\displaystyle \frac{\partial}{\partial x}g\frac{\partial}{\partial x} = \frac{\... ...ial g}{\partial x}\frac{\partial}{\partial x}+ g\frac{\partial^2}{\partial x^2}$