projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | <html> |
| 2 | <head> | |
| 3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
| 4 | <title>Using C++11 Lambda's</title> | |
| 5 | <link rel="stylesheet" href="../../../math.css" type="text/css"> | |
| 6 | <meta name="generator" content="DocBook XSL Stylesheets V1.77.1"> | |
| 7 | <link rel="home" href="../../../index.html" title="Math Toolkit 2.5.1"> | |
| 8 | <link rel="up" href="../root_finding_examples.html" title="Examples of Root-Finding (with and without derivatives)"> | |
| 9 | <link rel="prev" href="cbrt_eg.html" title="Finding the Cubed Root With and Without Derivatives"> | |
| 10 | <link rel="next" href="5th_root_eg.html" title="Computing the Fifth Root"> | |
| 11 | </head> | |
| 12 | <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> | |
| 13 | <table cellpadding="2" width="100%"><tr> | |
| 14 | <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> | |
| 15 | <td align="center"><a href="../../../../../../../index.html">Home</a></td> | |
| 16 | <td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> | |
| 17 | <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> | |
| 18 | <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> | |
| 19 | <td align="center"><a href="../../../../../../../more/index.htm">More</a></td> | |
| 20 | </tr></table> | |
| 21 | <hr> | |
| 22 | <div class="spirit-nav"> | |
| 23 | <a accesskey="p" href="cbrt_eg.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../root_finding_examples.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="5th_root_eg.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> | |
| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h4 class="title"> | |
| 27 | <a name="math_toolkit.roots.root_finding_examples.lambda"></a><a class="link" href="lambda.html" title="Using C++11 Lambda's">Using | |
| 28 | C++11 Lambda's</a> | |
| 29 | </h4></div></div></div> | |
| 30 | <p> | |
| 31 | Since all the root finding functions accept a function-object, they can | |
| 32 | be made to work (often in a lot less code) with C++11 lambda's. Here's | |
| 33 | the much reduced code for our "toy" cube root function: | |
| 34 | </p> | |
| 35 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> | |
| 36 | <span class="identifier">T</span> <span class="identifier">cbrt_2deriv_lambda</span><span class="special">(</span><span class="identifier">T</span> <span class="identifier">x</span><span class="special">)</span> | |
| 37 | <span class="special">{</span> | |
| 38 | <span class="comment">// return cube root of x using 1st and 2nd derivatives and Halley.</span> | |
| 39 | <span class="comment">//using namespace std; // Help ADL of std functions.</span> | |
| 40 | <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tools</span><span class="special">;</span> | |
| 41 | <span class="keyword">int</span> <span class="identifier">exponent</span><span class="special">;</span> | |
| 42 | <span class="identifier">frexp</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="special">&</span><span class="identifier">exponent</span><span class="special">);</span> <span class="comment">// Get exponent of z (ignore mantissa).</span> | |
| 43 | <span class="identifier">T</span> <span class="identifier">guess</span> <span class="special">=</span> <span class="identifier">ldexp</span><span class="special">(</span><span class="number">1.</span><span class="special">,</span> <span class="identifier">exponent</span> <span class="special">/</span> <span class="number">3</span><span class="special">);</span> <span class="comment">// Rough guess is to divide the exponent by three.</span> | |
| 44 | <span class="identifier">T</span> <span class="identifier">min</span> <span class="special">=</span> <span class="identifier">ldexp</span><span class="special">(</span><span class="number">0.5</span><span class="special">,</span> <span class="identifier">exponent</span> <span class="special">/</span> <span class="number">3</span><span class="special">);</span> <span class="comment">// Minimum possible value is half our guess.</span> | |
| 45 | <span class="identifier">T</span> <span class="identifier">max</span> <span class="special">=</span> <span class="identifier">ldexp</span><span class="special">(</span><span class="number">2.</span><span class="special">,</span> <span class="identifier">exponent</span> <span class="special">/</span> <span class="number">3</span><span class="special">);</span> <span class="comment">// Maximum possible value is twice our guess.</span> | |
| 46 | <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">digits</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">digits</span><span class="special">;</span> <span class="comment">// Maximum possible binary digits accuracy for type T.</span> | |
| 47 | <span class="comment">// digits used to control how accurate to try to make the result.</span> | |
| 48 | <span class="keyword">int</span> <span class="identifier">get_digits</span> <span class="special">=</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="identifier">digits</span> <span class="special">*</span> <span class="number">0.4</span><span class="special">);</span> <span class="comment">// Accuracy triples with each step, so stop when just</span> | |
| 49 | <span class="comment">// over one third of the digits are correct.</span> | |
| 50 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">uintmax_t</span> <span class="identifier">maxit</span> <span class="special">=</span> <span class="number">20</span><span class="special">;</span> | |
| 51 | <span class="identifier">T</span> <span class="identifier">result</span> <span class="special">=</span> <span class="identifier">halley_iterate</span><span class="special">(</span> | |
| 52 | <span class="comment">// lambda function:</span> | |
| 53 | <span class="special">[</span><span class="identifier">x</span><span class="special">](</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">g</span><span class="special">){</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_tuple</span><span class="special">(</span><span class="identifier">g</span> <span class="special">*</span> <span class="identifier">g</span> <span class="special">*</span> <span class="identifier">g</span> <span class="special">-</span> <span class="identifier">x</span><span class="special">,</span> <span class="number">3</span> <span class="special">*</span> <span class="identifier">g</span> <span class="special">*</span> <span class="identifier">g</span><span class="special">,</span> <span class="number">6</span> <span class="special">*</span> <span class="identifier">g</span><span class="special">);</span> <span class="special">},</span> | |
| 54 | <span class="identifier">guess</span><span class="special">,</span> <span class="identifier">min</span><span class="special">,</span> <span class="identifier">max</span><span class="special">,</span> <span class="identifier">get_digits</span><span class="special">,</span> <span class="identifier">maxit</span><span class="special">);</span> | |
| 55 | <span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span> | |
| 56 | <span class="special">}</span> | |
| 57 | </pre> | |
| 58 | <p> | |
| 59 | Full code of this example is at <a href="../../../../../example/root_finding_example.cpp" target="_top">root_finding_example.cpp</a>, | |
| 60 | </p> | |
| 61 | </div> | |
| 62 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 63 | <td align="left"></td> | |
| 64 | <td align="right"><div class="copyright-footer">Copyright © 2006-2010, 2012-2014 Nikhar Agrawal, | |
| 65 | Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, Hubert | |
| 66 | Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Johan Råde, Gautam Sewani, | |
| 67 | Benjamin Sobotta, Thijs van den Berg, Daryle Walker and Xiaogang Zhang<p> | |
| 68 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 69 | file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) | |
| 70 | </p> | |
| 71 | </div></td> | |
| 72 | </tr></table> | |
| 73 | <hr> | |
| 74 | <div class="spirit-nav"> | |
| 75 | <a accesskey="p" href="cbrt_eg.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../root_finding_examples.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="5th_root_eg.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> | |
| 76 | </div> | |
| 77 | </body> | |
| 78 | </html> |