Mathematical Methods in Chemical Engineering

2.5: SOME EXAMPLES

2.5 SOME EXAMPLES

In this section we consider two examples. In the first we simply develop the successive approximations without concern for their domain of validity, while in the second we also examine this aspect.

Example 1

For the linear ODE


with IC


construct the solution by successive approximations.

The analytic solution is readily obtained as


and let us now develop the successive approximations.

The function f( x, y) = y is continuous and satisfies the Lipschitz condition (with K = 1 + ?, where ? > 0) for = { x ?( ? ?, ?)}. The successive approximations are given by


Thus we have


and


Taking the limit as n ? ? yields


as expected.

Example 2

For the ODE


with IC


construct the successive approximations, and find the largest range of x for the solution.

The analytic solution can again be obtained easily by separation of variables:


which is clearly continuous for ? ? < x < 1, a range that contains the initial value of x (i.e., x = 0). A plot of eq. (2.5.8) is shown in Figure 2.3.


Figure 2.3: Plot of the exact solution and domain for Example 2.

The nonlinear function f( x, y) = y 2 is continuous for all x and y. It also satisfies the Lipschitz condition for all y, since


so that max[2 y +

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