Mon, 09 Nov 2015 13:45:10 -0800
Merge
1 /*
2 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
3 *
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9 * notice, this list of conditions and the following disclaimer.
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13 * documentation and/or other materials provided with the distribution.
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17 * from this software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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30 */
32 // Simple sample demonstrating "fixed point" computation with Streams
34 // See also https://mitpress.mit.edu/sicp/chapter1/node21.html#secprocgeneralmethods
35 var Stream = Java.type("java.util.stream.Stream");
37 // generic fixed point procedure
38 function fixed_point(f, init_guess) {
39 var tolerance = 0.00001;
40 function close_enough(v1, v2) Math.abs(v1 - v2) < tolerance;
42 var prev;
43 return Stream.iterate(init_guess, f)
44 .filter(function(x) {
45 try {
46 return prev == undefined? false : close_enough(prev, x);
47 } finally {
48 prev = x;
49 }
50 })
51 .findFirst()
52 .get();
53 }
55 // solution to x = cos(x)
56 print(fixed_point(Math.cos, 1.0))
58 // solution to x = sin(x) + cos(x)
59 print(fixed_point(function(x) Math.sin(x) + Math.cos(x), 1.0));
61 // square root by Newton's method
62 // http://en.wikipedia.org/wiki/Newton's_method
63 function sqrt(n)
64 fixed_point(function(x) (x + n/x) / 2, 2.0);
66 print(sqrt(2))
67 print(sqrt(3))