diff -r b129e9cbab87 -r 3f4320a01539 samples/fixed_point.js --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/samples/fixed_point.js Fri Sep 04 17:17:44 2015 +0530 @@ -0,0 +1,69 @@ +/* + * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * - Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * - Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * 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 + * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR + * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, + * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, + * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR + * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF + * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING + * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS + * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +// 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)) + +