70 lines
2.5 KiB
JavaScript
70 lines
2.5 KiB
JavaScript
/*
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* Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* - Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* - Neither the name of Oracle nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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// Simple sample demonstrating "fixed point" computation with Streams
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// See also https://mitpress.mit.edu/sicp/chapter1/node21.html#secprocgeneralmethods
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var Stream = Java.type("java.util.stream.Stream");
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// generic fixed point procedure
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function fixed_point(f, init_guess) {
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var tolerance = 0.00001;
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function close_enough(v1, v2) Math.abs(v1 - v2) < tolerance;
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var prev;
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return Stream.iterate(init_guess, f)
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.filter(function(x) {
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try {
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return prev == undefined? false : close_enough(prev, x);
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} finally {
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prev = x;
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}
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})
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.findFirst()
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.get();
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}
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// solution to x = cos(x)
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print(fixed_point(Math.cos, 1.0))
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// solution to x = sin(x) + cos(x)
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print(fixed_point(function(x) Math.sin(x) + Math.cos(x), 1.0));
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// square root by Newton's method
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// http://en.wikipedia.org/wiki/Newton's_method
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function sqrt(n)
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fixed_point(function(x) (x + n/x) / 2, 2.0);
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print(sqrt(2))
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print(sqrt(3))
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