| /* |
| * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved. |
| * |
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| * modification, are permitted provided that the following conditions |
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| * notice, this list of conditions and the following disclaimer. |
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| * - Redistributions in binary form must reproduce the above copyright |
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| * documentation and/or other materials provided with the distribution. |
| * |
| * - Neither the name of Oracle nor the names of its |
| * contributors may be used to endorse or promote products derived |
| * from this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS |
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| */ |
| |
| // Simple sample demonstrating "fixed point" computation with Streams |
| |
| // See also https://mitpress.mit.edu/sicp/chapter1/node21.html#secprocgeneralmethods |
| var Stream = Java.type("java.util.stream.Stream"); |
| |
| // generic fixed point procedure |
| function fixed_point(f, init_guess) { |
| var tolerance = 0.00001; |
| function close_enough(v1, v2) Math.abs(v1 - v2) < tolerance; |
| |
| var prev; |
| return Stream.iterate(init_guess, f) |
| .filter(function(x) { |
| try { |
| return prev == undefined? false : close_enough(prev, x); |
| } finally { |
| prev = x; |
| } |
| }) |
| .findFirst() |
| .get(); |
| } |
| |
| // solution to x = cos(x) |
| print(fixed_point(Math.cos, 1.0)) |
| |
| // solution to x = sin(x) + cos(x) |
| print(fixed_point(function(x) Math.sin(x) + Math.cos(x), 1.0)); |
| |
| // square root by Newton's method |
| // http://en.wikipedia.org/wiki/Newton's_method |
| function sqrt(n) |
| fixed_point(function(x) (x + n/x) / 2, 2.0); |
| |
| print(sqrt(2)) |
| print(sqrt(3)) |
| |
| |