1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
|
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Setting Policies at Namespace or Translation Unit Scope</title>
<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.76.1">
<link rel="home" href="../../../index.html" title="Math Toolkit">
<link rel="up" href="../pol_tutorial.html" title="Policy Tutorial">
<link rel="prev" href="ad_hoc_sf_policies.html" title="Changing the Policy on an Ad Hoc Basis for the Special Functions">
<link rel="next" href="user_def_err_pol.html" title="Calling User Defined Error Handlers">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td>
<td align="center"><a href="../../../../../../../../index.html">Home</a></td>
<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="ad_hoc_sf_policies.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../pol_tutorial.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="user_def_err_pol.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section math_toolkit_policy_pol_tutorial_namespace_policies">
<div class="titlepage"><div><div><h4 class="title">
<a name="math_toolkit.policy.pol_tutorial.namespace_policies"></a><a class="link" href="namespace_policies.html" title="Setting Policies at Namespace or Translation Unit Scope">Setting
Policies at Namespace or Translation Unit Scope</a>
</h4></div></div></div>
<p>
Sometimes what you want to do is just change a set of policies within the
current scope: <span class="bold"><strong>the one thing you should not do in
this situation is use the configuration macros</strong></span>, as this can
lead to "One Definition Rule" violations. Instead this library
provides a pair of macros especially for this purpose.
</p>
<p>
Let's consider the special functions first: we can declare a set of forwarding
functions that all use a specific policy using the macro BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS(<span class="emphasis"><em>Policy</em></span>).
This macro should be used either inside a unique namespace set aside for
the purpose (for example, a C namespace for a C-style policy), or an unnamed
namespace if you just want the functions visible in global scope for the
current file only.
</p>
<p>
Suppose we want <code class="computeroutput"><span class="identifier">C</span><span class="special">::</span><span class="identifier">foo</span><span class="special">()</span></code>
to behave in a C-compatible way and set <code class="computeroutput"><span class="special">::</span><span class="identifier">errno</span></code> on error rather than throwing any
exceptions.
</p>
<p>
We'll begin by including the needed header for our function:
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">special_functions</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="comment">//using boost::math::tgamma; // Not needed because using C::tgamma.</span></pre>
<p>
</p>
<p>
Open up the "C" namespace that we'll use for our functions, and
define the policy type we want: in this case a C-style one that sets ::errno
and returns a standard value, rather than throwing exceptions.
</p>
<p>
Any policies we don't specify here will inherit the defaults.
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">C</span>
<span class="special">{</span> <span class="comment">// To hold our C-style policy.</span>
<span class="comment">//using namespace boost::math::policies; or explicitly:</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">domain_error</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">pole_error</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">overflow_error</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">evaluation_error</span><span class="special">;</span>
<span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">errno_on_error</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span>
<span class="identifier">domain_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">>,</span>
<span class="identifier">pole_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">>,</span>
<span class="identifier">overflow_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">>,</span>
<span class="identifier">evaluation_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">></span>
<span class="special">></span> <span class="identifier">c_policy</span><span class="special">;</span></pre>
<p>
</p>
<p>
All we need do now is invoke the BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS macro
passing our policy type c_policy as the single argument:
</p>
<p>
</p>
<pre class="programlisting"><span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">c_policy</span><span class="special">)</span>
<span class="special">}</span> <span class="comment">// close namespace C</span></pre>
<p>
</p>
<p>
We now have a set of forwarding functions defined in namespace C that all
look something like this:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">RealType</span><span class="special">></span>
<span class="keyword">inline</span> <span class="keyword">typename</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><span class="identifier">promote_args</span><span class="special"><</span><span class="identifier">RT</span><span class="special">>::</span><span class="identifier">type</span>
<span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">RT</span> <span class="identifier">z</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">,</span> <span class="identifier">c_policy</span><span class="special">());</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
So that when we call <code class="computeroutput"><span class="identifier">C</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">)</span></code>,
we really end up calling <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">,</span>
<span class="identifier">C</span><span class="special">::</span><span class="identifier">c_policy</span><span class="special">())</span></code>:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">errno</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of tgamma(30000) is: "</span>
<span class="special"><<</span> <span class="identifier">C</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="number">30000</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> <span class="comment">// Note using C::tgamma</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"errno = "</span> <span class="special"><<</span> <span class="identifier">errno</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> <span class="comment">// errno = 34</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of tgamma(-10) is: "</span>
<span class="special"><<</span> <span class="identifier">C</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(-</span><span class="number">10</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"errno = "</span> <span class="special"><<</span> <span class="identifier">errno</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> <span class="comment">// errno = 33, overwriting previous value of 34.</span>
<span class="special">}</span></pre>
<p>
</p>
<p>
Which outputs:
</p>
<pre class="programlisting">Result of C::tgamma(30000) is: 1.#INF
errno = 34
Result of C::tgamma(-10) is: 1.#QNAN
errno = 33
</pre>
<p>
This mechanism is particularly useful when we want to define a project-wide
policy, and don't want to modify the Boost source, or to set project wide
build macros (possibly fragile and easy to forget).
</p>
<p>
The same mechanism works well at file scope as well, by using an unnamed
namespace, we can ensure that these declarations don't conflict with any
alternate policies present in other translation units:
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">special_functions</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="comment">// using boost::math::tgamma; // Would create an ambiguity between</span>
<span class="comment">// 'double boost::math::tgamma<int>(T)' and</span>
<span class="comment">// 'double 'anonymous-namespace'::tgamma<int>(RT)'.</span>
<span class="keyword">namespace</span>
<span class="special">{</span> <span class="comment">// unnamed</span>
<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">policies</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span>
<span class="identifier">domain_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">>,</span>
<span class="identifier">pole_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">>,</span>
<span class="identifier">overflow_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">>,</span>
<span class="identifier">evaluation_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">></span>
<span class="special">></span> <span class="identifier">c_policy</span><span class="special">;</span>
<span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">c_policy</span><span class="special">)</span></pre>
<p>
</p>
<p>
So that when we call <code class="computeroutput"><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">)</span></code>,
we really end up calling <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">,</span>
<span class="identifier">anonymous</span><span class="special">-</span><span class="keyword">namespace</span><span class="special">::</span><span class="identifier">c_policy</span><span class="special">())</span></code>.
</p>
<p>
</p>
<pre class="programlisting"><span class="special">}</span> <span class="comment">// close unnamed namespace</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">errno</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of tgamma(30000) is: "</span>
<span class="special"><<</span> <span class="identifier">tgamma</span><span class="special">(</span><span class="number">30000</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="comment">// tgamma in unnamed namespace in this translation unit (file) only.</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"errno = "</span> <span class="special"><<</span> <span class="identifier">errno</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of tgamma(-10) is: "</span>
<span class="special"><<</span> <span class="identifier">tgamma</span><span class="special">(-</span><span class="number">10</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"errno = "</span> <span class="special"><<</span> <span class="identifier">errno</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="comment">// Default tgamma policy would throw an exception, and abort.</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
Handling policies for the statistical distributions is very similar except
that now the macro BOOST_MATH_DECLARE_DISTRIBUTIONS accepts two parameters:
the floating point type to use, and the policy type to apply. For example:
</p>
<pre class="programlisting"><span class="identifier">BOOST_MATH_DECLARE_DISTRIBUTIONS</span><span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">mypolicy</span><span class="special">)</span>
</pre>
<p>
Results a set of typedefs being defined like this:
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">normal_distribution</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">mypolicy</span><span class="special">></span> <span class="identifier">normal</span><span class="special">;</span>
</pre>
<p>
The name of each typedef is the same as the name of the distribution class
template, but without the "_distribution" suffix.
</p>
<p>
Suppose we want a set of distributions to behave as follows:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
Return infinity on overflow, rather than throwing an exception.
</li>
<li class="listitem">
Don't perform any promotion from double to long double internally.
</li>
<li class="listitem">
Return the closest integer result from the quantiles of discrete distributions.
</li>
</ul></div>
<p>
We'll begin by including the needed header for all the distributions:
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">distributions</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre>
<p>
</p>
<p>
Open up an appropriate namespace, calling it <code class="computeroutput"><span class="identifier">my_distributions</span></code>,
for our distributions, and define the policy type we want. Any policies
we don't specify here will inherit the defaults:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">my_distributions</span>
<span class="special">{</span>
<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">policies</span><span class="special">;</span>
<span class="comment">// using boost::math::policies::errno_on_error; // etc.</span>
<span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span>
<span class="comment">// return infinity and set errno rather than throw:</span>
<span class="identifier">overflow_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">>,</span>
<span class="comment">// Don't promote double -> long double internally:</span>
<span class="identifier">promote_double</span><span class="special"><</span><span class="keyword">false</span><span class="special">>,</span>
<span class="comment">// Return the closest integer result for discrete quantiles:</span>
<span class="identifier">discrete_quantile</span><span class="special"><</span><span class="identifier">integer_round_nearest</span><span class="special">></span>
<span class="special">></span> <span class="identifier">my_policy</span><span class="special">;</span></pre>
<p>
</p>
<p>
All we need do now is invoke the BOOST_MATH_DECLARE_DISTRIBUTIONS macro
passing the floating point type <code class="computeroutput"><span class="keyword">double</span></code>
and policy types <code class="computeroutput"><span class="identifier">my_policy</span></code>
as arguments:
</p>
<p>
</p>
<pre class="programlisting"><span class="identifier">BOOST_MATH_DECLARE_DISTRIBUTIONS</span><span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">)</span>
<span class="special">}</span> <span class="comment">// close namespace my_namespace</span></pre>
<p>
</p>
<p>
We now have a set of typedefs defined in namespace my_distributions that
all look something like this:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">normal_distribution</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></span> <span class="identifier">normal</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">cauchy_distribution</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></span> <span class="identifier">cauchy</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">gamma_distribution</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></span> <span class="identifier">gamma</span><span class="special">;</span>
<span class="comment">// etc</span>
</pre>
<p>
</p>
<p>
So that when we use my_distributions::normal we really end up using <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">normal_distribution</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">></span></code>:
</p>
<p>
</p>
<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">// Construct distribution with something we know will overflow</span>
<span class="comment">// (using double rather than if promoted to long double):</span>
<span class="identifier">my_distributions</span><span class="special">::</span><span class="identifier">normal</span> <span class="identifier">norm</span><span class="special">(</span><span class="number">10</span><span class="special">,</span> <span class="number">2</span><span class="special">);</span>
<span class="identifier">errno</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of quantile(norm, 0) is: "</span>
<span class="special"><<</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">norm</span><span class="special">,</span> <span class="number">0</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> <span class="comment">// -infinity.</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"errno = "</span> <span class="special"><<</span> <span class="identifier">errno</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">errno</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of quantile(norm, 1) is: "</span>
<span class="special"><<</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">norm</span><span class="special">,</span> <span class="number">1</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> <span class="comment">// +infinity.</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"errno = "</span> <span class="special"><<</span> <span class="identifier">errno</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="comment">// Now try a discrete distribution.</span>
<span class="identifier">my_distributions</span><span class="special">::</span><span class="identifier">binomial</span> <span class="identifier">binom</span><span class="special">(</span><span class="number">20</span><span class="special">,</span> <span class="number">0.25</span><span class="special">);</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of quantile(binom, 0.05) is: "</span>
<span class="special"><<</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">binom</span><span class="special">,</span> <span class="number">0.05</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> <span class="comment">// To check we get integer results.</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of quantile(complement(binom, 0.05)) is: "</span>
<span class="special"><<</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">complement</span><span class="special">(</span><span class="identifier">binom</span><span class="special">,</span> <span class="number">0.05</span><span class="special">))</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span></pre>
<p>
</p>
<p>
Which outputs:
</p>
<pre class="programlisting">Result of quantile(norm, 0) is: -1.#INF
errno = 34
Result of quantile(norm, 1) is: 1.#INF
errno = 34
Result of quantile(binom, 0.05) is: 1
Result of quantile(complement(binom, 0.05)) is: 8
</pre>
<p>
This mechanism is particularly useful when we want to define a project-wide
policy, and don't want to modify the Boost source or set project wide build
macros (possibly fragile and easy to forget).
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
There is an important limitation to note: you can *not use the macros
BOOST_MATH_DECLARE_DISTRIBUTIONS and BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS
<span class="emphasis"><em>in the same namespace</em></span>*, as doing so creates ambiguities
between functions and distributions of the same name.
</p></td></tr>
</table></div>
<p>
As before, the same mechanism works well at file scope as well: by using
an unnamed namespace, we can ensure that these declarations don't conflict
with any alternate policies present in other translation units:
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">distributions</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> <span class="comment">// All distributions.</span>
<span class="comment">// using boost::math::normal; // Would create an ambguity between</span>
<span class="comment">// boost::math::normal_distribution<RealType> boost::math::normal and</span>
<span class="comment">// 'anonymous-namespace'::normal'.</span>
<span class="keyword">namespace</span>
<span class="special">{</span> <span class="comment">// anonymous or unnnamed (rather than named as in policy_eg_6.cpp).</span>
<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">policies</span><span class="special">;</span>
<span class="comment">// using boost::math::policies::errno_on_error; // etc.</span>
<span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span>
<span class="comment">// return infinity and set errno rather than throw:</span>
<span class="identifier">overflow_error</span><span class="special"><</span><span class="identifier">errno_on_error</span><span class="special">>,</span>
<span class="comment">// Don't promote double -> long double internally:</span>
<span class="identifier">promote_double</span><span class="special"><</span><span class="keyword">false</span><span class="special">>,</span>
<span class="comment">// Return the closest integer result for discrete quantiles:</span>
<span class="identifier">discrete_quantile</span><span class="special"><</span><span class="identifier">integer_round_nearest</span><span class="special">></span>
<span class="special">></span> <span class="identifier">my_policy</span><span class="special">;</span>
<span class="identifier">BOOST_MATH_DECLARE_DISTRIBUTIONS</span><span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">my_policy</span><span class="special">)</span>
<span class="special">}</span> <span class="comment">// close namespace my_namespace</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">// Construct distribution with something we know will overflow.</span>
<span class="identifier">normal</span> <span class="identifier">norm</span><span class="special">(</span><span class="number">10</span><span class="special">,</span> <span class="number">2</span><span class="special">);</span> <span class="comment">// using 'anonymous-namespace'::normal</span>
<span class="identifier">errno</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of quantile(norm, 0) is: "</span>
<span class="special"><<</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">norm</span><span class="special">,</span> <span class="number">0</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"errno = "</span> <span class="special"><<</span> <span class="identifier">errno</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">errno</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of quantile(norm, 1) is: "</span>
<span class="special"><<</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">norm</span><span class="special">,</span> <span class="number">1</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"errno = "</span> <span class="special"><<</span> <span class="identifier">errno</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="comment">//</span>
<span class="comment">// Now try a discrete distribution:</span>
<span class="identifier">binomial</span> <span class="identifier">binom</span><span class="special">(</span><span class="number">20</span><span class="special">,</span> <span class="number">0.25</span><span class="special">);</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of quantile(binom, 0.05) is: "</span>
<span class="special"><<</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">binom</span><span class="special">,</span> <span class="number">0.05</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of quantile(complement(binom, 0.05)) is: "</span>
<span class="special"><<</span> <span class="identifier">quantile</span><span class="special">(</span><span class="identifier">complement</span><span class="special">(</span><span class="identifier">binom</span><span class="special">,</span> <span class="number">0.05</span><span class="special">))</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2006-2010 John Maddock, Paul A. Bristow, Hubert Holin, Xiaogang Zhang, Bruno
Lalande, Johan Råde, Gautam Sewani and Thijs van den Berg<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
</p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="ad_hoc_sf_policies.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../pol_tutorial.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="user_def_err_pol.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
|
