and so on. Substituting u(x) and its derivatives in the given differential equa-
tion, and equating coefficients of like powers of x gives a recurrence relation
that can be solved to determine the coefficients an , n 0. Substituting the
obtained values of an , n 0 in the series assumption (1.82) gives the series
solution. As stated before, the series may converge to the exact solution. Oth-
erwise, the obtained series can be truncated to any finite number of terms to
be used for numerical calculations. The more terms we use will enhance the
level of accuracy of the numerical approximation.
It is interesting to point out that the series solution method can be used
for homogeneous and inhomogeneous equations as well when x = 0 is an
ordinary point. However, if x = 0 is a regular singular point of an ODE, then
solution can be obtained by Frobenius method that will not be reviewed in
this text. Moreover, the Taylor series of any elementary function involved in
the differential equation should be used for equating the coefficients.
The series solution method will be illustrated by examining the following
ordinary differential equations where x = 0 is an ordinary point. Some ex-
amples will give exact solutions, whereas others will provide series solutions
that can be used for numerical purposes.