ABSTRACT
Any equation involving derivatives is called a differential equation. If there is only one independent variable the equation is termed a total differential equation or an ordinary differential equation. If there is more than one independent variable the equation is called a partial differential equation. If the highest-order derivative is the nth then the equation is said to be nth order. If there is no function of the dependent variable and its derivatives other than the linear one, the equation is said to be linear. The solution of differential equations can only be obtained in closed form in special cases. For all others, series or approximate or numerical solutions are necessary. The study of partial differential equations is of continuing interest in applications.
