In mathematics, any combination of derivatives applied to a function .
It takes the form of a polynomial of derivatives, such as D 2 x x - D 2 x y · D 2 y x , where D 2 is a second derivative and the subscripts indicate gradient , divergence , curl , and Laplace operator (see Laplace's equation ). Differential operators provide a generalized way to look at differentiation as a whole, as well as a framework for discussion of the theory of {{link=differential equation">differential equations .