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The Computable Differential Equation Lecture ... - Bruce E. Shapiro

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46 CHAPTER 3. APPROXIMATE SOLUTIONS<br />

y 3 = y 2 + hf(t 2 , y 2 ) (3.26)<br />

= 1.5625 + (0.25)(1.5625) = 1.953125 (3.27)<br />

t 3 = t 2 + h = 0.5 + 0.25 = 0.75 (3.28)<br />

(t 3 , y 3 ) = (0.75, 1.953125) (3.29)<br />

y 4 = y 3 + hf(t 3 , y 3 ) (3.30)<br />

= 1.953125 + (0.25)(1.953125) = 2.44140625 (3.31)<br />

t 4 = t 3 + 0.25 = 1.0 (3.32)<br />

(t 4 , y 4 ) = (1.0, 2.44140625) (3.33)<br />

Since t 4 = 1 we are done. <strong>The</strong> solutions are tabulated in table 3.1 for this and<br />

other step sizes. <strong>The</strong>se solutions are also illustrated in figure 3.1. <strong>The</strong> green dots in<br />

the figure correspond to the numbers calculated here; the other colors correspond<br />

to other step sizes. <strong>The</strong> points are joined by straight lines in the figure, but the<br />

straight lines are not part of the solution, only the dots. <strong>The</strong> figure also shows the<br />

exact solution.<br />

Table 3.1: Approximate values for different step sizes. See example 3.1.<br />

t h = 1/2 h = 1/4 h = 1/8 h = 1/16 exact solution<br />

0.0000 1.0000 1.0000 1.0000 1.0000 1.0000<br />

0.0625 1.0625 1.0645<br />

0.1250 1.1250 1.1289 1.1331<br />

0.1875 1.1995 1.2062<br />

0.2500 1.2500 1.2656 1.2744 1.2840<br />

0.3125 1.3541 1.3668<br />

0.3750 1.4238 1.4387 1.4550<br />

0.4375 1.5286 1.5488<br />

0.5000 1.5000 1.5625 1.6018 1.6242 1.6487<br />

0.5625 1.7257 1.7551<br />

0.6250 1.8020 1.8335 1.8682<br />

0.6875 1.9481 1.9887<br />

0.7500 1.9531 2.0273 2.0699 2.1170<br />

0.8125 2.1993 2.2535<br />

0.8750 2.2807 2.3367 2.3989<br />

0.9375 2.4828 2.5536<br />

1.0000 2.2500 2.4414 2.5658 2.6379 2.7183<br />

Math 582B, Spring 2007<br />

California State University Northridge<br />

c○2007, B.E.<strong>Shapiro</strong><br />

Last revised: May 23, 2007

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