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1 /* |
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2 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved. |
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3 * |
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4 * Redistribution and use in source and binary forms, with or without |
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5 * modification, are permitted provided that the following conditions |
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6 * are met: |
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7 * |
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8 * - Redistributions of source code must retain the above copyright |
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9 * notice, this list of conditions and the following disclaimer. |
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10 * |
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11 * - Redistributions in binary form must reproduce the above copyright |
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12 * notice, this list of conditions and the following disclaimer in the |
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13 * documentation and/or other materials provided with the distribution. |
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14 * |
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15 * - Neither the name of Oracle nor the names of its |
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16 * contributors may be used to endorse or promote products derived |
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17 * from this software without specific prior written permission. |
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18 * |
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19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS |
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20 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, |
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21 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
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22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR |
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23 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
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24 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
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25 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
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26 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF |
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27 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING |
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28 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS |
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29 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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30 */ |
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31 |
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32 // Simple sample demonstrating "fixed point" computation with Streams |
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33 |
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34 // See also https://mitpress.mit.edu/sicp/chapter1/node21.html#secprocgeneralmethods |
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35 var Stream = Java.type("java.util.stream.Stream"); |
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36 |
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37 // generic fixed point procedure |
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38 function fixed_point(f, init_guess) { |
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39 var tolerance = 0.00001; |
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40 function close_enough(v1, v2) Math.abs(v1 - v2) < tolerance; |
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41 |
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42 var prev; |
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43 return Stream.iterate(init_guess, f) |
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44 .filter(function(x) { |
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45 try { |
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46 return prev == undefined? false : close_enough(prev, x); |
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47 } finally { |
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48 prev = x; |
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49 } |
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50 }) |
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51 .findFirst() |
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52 .get(); |
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53 } |
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54 |
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55 // solution to x = cos(x) |
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56 print(fixed_point(Math.cos, 1.0)) |
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57 |
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58 // solution to x = sin(x) + cos(x) |
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59 print(fixed_point(function(x) Math.sin(x) + Math.cos(x), 1.0)); |
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60 |
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61 // square root by Newton's method |
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62 // http://en.wikipedia.org/wiki/Newton's_method |
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63 function sqrt(n) |
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64 fixed_point(function(x) (x + n/x) / 2, 2.0); |
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65 |
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66 print(sqrt(2)) |
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67 print(sqrt(3)) |
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68 |
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69 |