Читать книгу An Introduction to the Finite Element Method for Differential Equations - Mohammad Asadzadeh - Страница 16

A function of one real variable is said to be of class on an open interval if its derivatives exist and are continuous on . A function of real variables is said to be of class on a set if all of its partial derivatives of order , i.e. with the multi‐index and , exist and are continuous on .

As we mentioned, a key defining property of a PDE is that there are derivatives with respect to more than one independent variable and a PDE is a relation between an unknown function and its partial derivatives:

(1.3.1)