1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/samples/fixed_point.js Fri Sep 04 17:17:44 2015 +0530
1.3 @@ -0,0 +1,69 @@
1.4 +/*
1.5 + * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
1.6 + *
1.7 + * Redistribution and use in source and binary forms, with or without
1.8 + * modification, are permitted provided that the following conditions
1.9 + * are met:
1.10 + *
1.11 + * - Redistributions of source code must retain the above copyright
1.12 + * notice, this list of conditions and the following disclaimer.
1.13 + *
1.14 + * - Redistributions in binary form must reproduce the above copyright
1.15 + * notice, this list of conditions and the following disclaimer in the
1.16 + * documentation and/or other materials provided with the distribution.
1.17 + *
1.18 + * - Neither the name of Oracle nor the names of its
1.19 + * contributors may be used to endorse or promote products derived
1.20 + * from this software without specific prior written permission.
1.21 + *
1.22 + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
1.23 + * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
1.24 + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
1.25 + * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
1.26 + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
1.27 + * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
1.28 + * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
1.29 + * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
1.30 + * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
1.31 + * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
1.32 + * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.33 + */
1.34 +
1.35 +// Simple sample demonstrating "fixed point" computation with Streams
1.36 +
1.37 +// See also https://mitpress.mit.edu/sicp/chapter1/node21.html#secprocgeneralmethods
1.38 +var Stream = Java.type("java.util.stream.Stream");
1.39 +
1.40 +// generic fixed point procedure
1.41 +function fixed_point(f, init_guess) {
1.42 + var tolerance = 0.00001;
1.43 + function close_enough(v1, v2) Math.abs(v1 - v2) < tolerance;
1.44 +
1.45 + var prev;
1.46 + return Stream.iterate(init_guess, f)
1.47 + .filter(function(x) {
1.48 + try {
1.49 + return prev == undefined? false : close_enough(prev, x);
1.50 + } finally {
1.51 + prev = x;
1.52 + }
1.53 + })
1.54 + .findFirst()
1.55 + .get();
1.56 +}
1.57 +
1.58 +// solution to x = cos(x)
1.59 +print(fixed_point(Math.cos, 1.0))
1.60 +
1.61 +// solution to x = sin(x) + cos(x)
1.62 +print(fixed_point(function(x) Math.sin(x) + Math.cos(x), 1.0));
1.63 +
1.64 +// square root by Newton's method
1.65 +// http://en.wikipedia.org/wiki/Newton's_method
1.66 +function sqrt(n)
1.67 + fixed_point(function(x) (x + n/x) / 2, 2.0);
1.68 +
1.69 +print(sqrt(2))
1.70 +print(sqrt(3))
1.71 +
1.72 +
