Unformatted text preview: of axes ranges, and then narrow the view by choosing a smaller and smaller x-range.
[> plot( f(x), x=-10..10, y = -10..10);
[> plot( f(x), x=-4..4, y = -10..10);
[> plot( f(x), x=-1..1, y = -10..10);
iii Copyrighted by B.A. Forrest ([email protected]) Newton’s Method in Maple The plots indicate that f (x) crosses the x-axis in the interval [0, 1]. This will be our starting interval for the Bisection
You could also conﬁrm that f (x) changes sign over this interval by checking:
Note that Maple tells us that f (0) = −1 < 0 and f (1) = 1 > 0. This calculation conﬁrms that the root c lies somewhere
between 0 and 1. So, using the notation of the Bisection Method from before, let a = 0 and b = 1 (i.e., the endpoints of
To assign values to a variable in Maple, we use the assignment operator
In Maple, enter the following to assign values to “a” and ”b”:
[> a := 0;
[> b := 1.0; The midpoint d is found by calculating a+b
2. In Maple, this is: [> d := (a+b)/2;
Maple tells us that the midpoint of the interval [0, 1] is d = 0.5. We must next ﬁnd f (0.5) or equivalently, f (d) to continue with the algorithm and to ﬁnd the side of the interval on which
the midpoint c is located.
[> f(d); Maple tells us f (d) = f (0.5) = −0.46875. Since f (a) = f (0) < 0 from
above, the Bisection Method tells us to replace a by d. This means we
must assign a the current value of d.
[> a := d; Our current state in the Bisection Method is a = 0.5 and b = 1.0. We now know that c is located somewhere in the interval
To make sure we have not made any errors, let’s try plotting f (x) in the interval [0.5, 1.0].
[> plot( f(x), x=0.5..1.0);
(Indeed, we can see from the plot that c lies somewhere between 0.7 and 0.8.)
To reﬁne the search for c even further, we repeat this process with the new interval [0.5, 1.0]. The new midpoint is
[> d := (a+b)/2;
iv Copyrighted by B.A. Forrest ([email protected]) Newton’s Method in Maple Maple tells us that the new value of the midpoint d is 0.75. We again ﬁnd f (d).
Maple tells us f (d) = f (0.75) = −0.0126953125. Since, from before, we have f (a) = f (0.5) = −0.46875 < 0, the Bisection
Method tells us again to replace a by d. T...
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