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Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

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Sec. 5] Numerical Integration of Ord<strong>in</strong>ary Differential Equations_387<br />

If e/ does not exceed the unit of the last decimal \(y m reta<strong>in</strong>ed <strong>in</strong> the<br />

take I// and calculate the next value y/ + 1 ,<br />

- answer for y (x), then for f/ we t<br />

repeat<strong>in</strong>g the process. But if<br />

e/ > 10~ w then one has to start from the , be-<br />

g<strong>in</strong>n<strong>in</strong>g and reduce the <strong>in</strong>terval of calculations. The magnitude<br />

of the <strong>in</strong>itial<br />

<strong>in</strong>terval is determ<strong>in</strong>ed approximately from the <strong>in</strong>equality h 4 < 10~ m .<br />

For the case of a solution of the system (4), the Milne formulas are<br />

written separately for the functions y (x) and z (x). The order of calculations<br />

rema<strong>in</strong>s the same.<br />

Example 1. Given a differential equation */'=*/ x with the <strong>in</strong>itial condition<br />

y(0)=1.5. Calculate to two decimal places the value of the solution<br />

of this equation when the argument is x 1.5. Carry out the calculations<br />

by a comb<strong>in</strong>ed Runge-Kutta and Milne method.<br />

Solution. We choose the <strong>in</strong>itial <strong>in</strong>terval h from the condition /r*

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