Abdelrahman Said
1527 lines
57 KiB
HTML
1527 lines
57 KiB
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<html>
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<title>Chapter 8. Random numbers</title>
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<link rel="prev" href="igraph-Data-structures.html" title="Chapter 7. Data structure library: vector, matrix, other data types">
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<link rel="chapter" href="igraph-Random.html" title="Chapter 8. Random numbers">
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<link rel="chapter" href="igraph-Visitors.html" title="Chapter 16. Graph visitors">
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<link rel="chapter" href="igraph-Structural.html" title="Chapter 17. Structural properties of graphs">
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<link rel="chapter" href="igraph-Motifs.html" title="Chapter 20. Graph motifs, dyad census and triad census">
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<link rel="chapter" href="igraph-Isomorphism.html" title="Chapter 21. Graph isomorphism">
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<link rel="chapter" href="igraph-Flows.html" title="Chapter 23. Maximum flows, minimum cuts and related measures">
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<link rel="chapter" href="igraph-Separators.html" title="Chapter 24. Vertex separators">
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<link rel="chapter" href="igraph-Community.html" title="Chapter 25. Detecting community structure">
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<link rel="chapter" href="igraph-Graphlets.html" title="Chapter 26. Graphlets">
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<link rel="chapter" href="igraph-HRG.html" title="Chapter 27. Hierarchical random graphs">
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<link rel="chapter" href="igraph-Embedding.html" title="Chapter 28. Embedding of graphs">
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<link rel="chapter" href="igraph-Layout.html" title="Chapter 29. Generating layouts for graph drawing">
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<link rel="chapter" href="igraph-Processes.html" title="Chapter 30. Processes on graphs">
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<link rel="chapter" href="igraph-Foreign.html" title="Chapter 31. Reading and writing graphs from and to files">
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<link rel="chapter" href="igraph-Nongraph.html" title="Chapter 33. Non-graph related functions">
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<div class="chapter">
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<div class="titlepage"><div><div><h1 class="title">
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<a name="igraph-Random"></a>Chapter 8. Random numbers</h1></div></div></div>
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<div class="toc"><dl class="toc">
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<dt><span class="section"><a href="igraph-Random.html#about-random-numbers-in-igraph">1. About random numbers in igraph</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#default-random-number-generator">2. The default random number generator</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#creating-random-number-generators">3. Creating random number generators</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#generating-random-numbers">4. Generating random numbers</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#supported-random-number-generators">5. Supported random number generators</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#random-use-cases">6. Use cases</a></span></dt>
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</dl></div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="about-random-numbers-in-igraph"></a>1. About random numbers in igraph</h2></div></div></div>
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<p>
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Some algorithms in igraph, such as sampling from random graph models,
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require random number generators (RNGs). igraph includes a flexible
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RNG framework that allows hooking up arbitrary random number generators,
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and comes with several ready-to-use generators. This framework is used
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in igraph's high-level interfaces to integrate with the host language's
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own RNG.
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</p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="default-random-number-generator"></a>2. The default random number generator</h2></div></div></div>
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<div class="toc"><dl class="toc">
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<dt><span class="section"><a href="igraph-Random.html#igraph_rng_default">2.1. <code class="function">igraph_rng_default</code> — Query the default random number generator.</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#igraph_rng_set_default">2.2. <code class="function">igraph_rng_set_default</code> — Set the default igraph random number generator.</a></span></dt>
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</dl></div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="igraph_rng_default"></a>2.1. <code class="function">igraph_rng_default</code> — Query the default random number generator.</h3></div></div></div>
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<a class="indexterm" name="id-1.9.3.2.2"></a><p>
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</p>
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<div class="informalexample"><pre class="programlisting">
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igraph_rng_t *igraph_rng_default(void);
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</pre></div>
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<p>
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</p>
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<p>
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</p>
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<p><b>Returns: </b></p>
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<div class="variablelist"><table border="0" class="variablelist">
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<colgroup>
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<col align="left" valign="top">
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<col>
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</colgroup>
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<tbody><tr>
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<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
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<td><p>
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A pointer to the default random number generator.
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</p></td>
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</tr></tbody>
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</table></div>
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<p>
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</p>
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<p><b>See also: </b></p>
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<div class="variablelist"><table border="0" class="variablelist">
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<colgroup>
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<col align="left" valign="top">
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<col>
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</colgroup>
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<tbody><tr>
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<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
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<td><p>
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<a class="link" href="igraph-Random.html#igraph_rng_set_default" title="2.2. igraph_rng_set_default — Set the default igraph random number generator."><code class="function">igraph_rng_set_default()</code></a>
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</p></td>
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</tr></tbody>
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</table></div>
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<p>
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</p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="igraph_rng_set_default"></a>2.2. <code class="function">igraph_rng_set_default</code> — Set the default igraph random number generator.</h3></div></div></div>
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<a class="indexterm" name="id-1.9.3.3.2"></a><p>
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</p>
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<div class="informalexample"><pre class="programlisting">
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igraph_rng_t *igraph_rng_set_default(igraph_rng_t *rng);
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</pre></div>
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<p>
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</p>
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<p>
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This function updates the default RNG used by igraph to be the one
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pointed to by <em class="parameter"><code>rng</code></em>, and returns a pointer to the previous default
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RNG. Future calls to <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a> will return the same
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pointer as <em class="parameter"><code>rng</code></em>. The RNG pointed to by <em class="parameter"><code>rng</code></em> must not be destroyed
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for as long as it is used as the default.
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</p>
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<p><b>Arguments: </b>
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</p>
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<div class="variablelist"><table border="0" class="variablelist">
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<colgroup>
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<col align="left" valign="top">
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<col>
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</colgroup>
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<tbody><tr>
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<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
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<td><p>
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The random number generator to use as default from now
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on. Calling <a class="link" href="igraph-Random.html#igraph_rng_destroy" title="3.2. igraph_rng_destroy — Deallocates memory associated with a random number generator."><code class="function">igraph_rng_destroy()</code></a> on it, while it is still
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being used as the default will result in crashes and/or
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unpredictable results.
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</p></td>
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</tr></tbody>
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</table></div>
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<p>
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</p>
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<p><b>Returns: </b></p>
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<div class="variablelist"><table border="0" class="variablelist">
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<colgroup>
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<col align="left" valign="top">
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<col>
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</colgroup>
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<tbody><tr>
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<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
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<td><p>
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Pointer the previous default RNG.
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</p></td>
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</tr></tbody>
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</table></div>
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<p>
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Time complexity: O(1).
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</p>
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</div>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="creating-random-number-generators"></a>3. Creating random number generators</h2></div></div></div>
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<div class="toc"><dl class="toc">
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<dt><span class="section"><a href="igraph-Random.html#igraph_rng_init">3.1. <code class="function">igraph_rng_init</code> — Initializes a random number generator.</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#igraph_rng_destroy">3.2. <code class="function">igraph_rng_destroy</code> — Deallocates memory associated with a random number generator.</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#igraph_rng_seed">3.3. <code class="function">igraph_rng_seed</code> — Seeds a random number generator.</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#igraph_rng_bits">3.4. <code class="function">igraph_rng_bits</code> — The number of random bits that a random number generator can produces in a single round.</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#igraph_rng_max">3.5. <code class="function">igraph_rng_max</code> — The maximum possible integer for a random number generator.</a></span></dt>
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<dt><span class="section"><a href="igraph-Random.html#igraph_rng_name">3.6. <code class="function">igraph_rng_name</code> — The type of a random number generator.</a></span></dt>
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</dl></div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="igraph_rng_init"></a>3.1. <code class="function">igraph_rng_init</code> — Initializes a random number generator.</h3></div></div></div>
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<a class="indexterm" name="id-1.9.4.2.2"></a><p>
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</p>
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<div class="informalexample"><pre class="programlisting">
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igraph_error_t igraph_rng_init(igraph_rng_t *rng, const igraph_rng_type_t *type);
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</pre></div>
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<p>
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</p>
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<p>
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This function allocates memory for a random number generator, with
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the given type, and sets its seed to the default.
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</p>
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<p><b>Arguments: </b>
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</p>
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<div class="variablelist"><table border="0" class="variablelist">
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<colgroup>
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<col align="left" valign="top">
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<col>
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</colgroup>
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<tbody>
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<tr>
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<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
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<td><p>
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Pointer to an uninitialized RNG.
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</p></td>
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</tr>
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<tr>
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<td><p><span class="term"><em class="parameter"><code>type</code></em>:</span></p></td>
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<td><p>
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The type of the RNG, such as <a class="link" href="igraph-Random.html#igraph_rngtype_mt19937" title="5.1. igraph_rngtype_mt19937 — The MT19937 random number generator."><code class="function">igraph_rngtype_mt19937</code></a>,
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<a class="link" href="igraph-Random.html#igraph_rngtype_glibc2" title="5.2. igraph_rngtype_glibc2 — The random number generator introduced in GNU libc 2."><code class="function">igraph_rngtype_glibc2</code></a>, <a class="link" href="igraph-Random.html#igraph_rngtype_pcg32" title="5.3. igraph_rngtype_pcg32 — The PCG random number generator (32-bit version)."><code class="function">igraph_rngtype_pcg32</code></a> or
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<a class="link" href="igraph-Random.html#igraph_rngtype_pcg64" title="5.4. igraph_rngtype_pcg64 — The PCG random number generator (64-bit version)."><code class="function">igraph_rngtype_pcg64</code></a>.
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</p></td>
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</tr>
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</tbody>
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</table></div>
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<p>
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</p>
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<p><b>Returns: </b></p>
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<div class="variablelist"><table border="0" class="variablelist">
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<colgroup>
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<col align="left" valign="top">
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<col>
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</colgroup>
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<tbody><tr>
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<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
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<td><p>
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Error code.
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</p></td>
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</tr></tbody>
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</table></div>
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<p>
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</p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="igraph_rng_destroy"></a>3.2. <code class="function">igraph_rng_destroy</code> — Deallocates memory associated with a random number generator.</h3></div></div></div>
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<a class="indexterm" name="id-1.9.4.3.2"></a><p>
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</p>
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<div class="informalexample"><pre class="programlisting">
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void igraph_rng_destroy(igraph_rng_t *rng);
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</pre></div>
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<p>
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</p>
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<p>
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||
|
||
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||
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</p>
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<p><b>Arguments: </b>
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</p>
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||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
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<col align="left" valign="top">
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||
<col>
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||
</colgroup>
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||
<tbody><tr>
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<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
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<td><p>
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The RNG to destroy. Do not destroy an RNG that is used
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as the default igraph RNG.</p></td>
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</tr></tbody>
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||
</table></div>
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<p>
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Time complexity: O(1).
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</p>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="igraph_rng_seed"></a>3.3. <code class="function">igraph_rng_seed</code> — Seeds a random number generator.</h3></div></div></div>
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||
<a class="indexterm" name="id-1.9.4.4.2"></a><p>
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||
</p>
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||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_error_t igraph_rng_seed(igraph_rng_t *rng, igraph_uint_t seed);
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</pre></div>
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||
<p>
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||
</p>
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||
<p>
|
||
|
||
|
||
|
||
</p>
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<p><b>Arguments: </b>
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</p>
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<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
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||
<col align="left" valign="top">
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||
<col>
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||
</colgroup>
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||
<tbody>
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<tr>
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<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
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<td><p>
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The RNG.
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</p></td>
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</tr>
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<tr>
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<td><p><span class="term"><em class="parameter"><code>seed</code></em>:</span></p></td>
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<td><p>
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The new seed.
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</p></td>
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</tr>
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</tbody>
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</table></div>
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<p>
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</p>
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<p><b>Returns: </b></p>
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<div class="variablelist"><table border="0" class="variablelist">
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<colgroup>
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<col align="left" valign="top">
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<col>
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</colgroup>
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<tbody><tr>
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<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
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<td><p>
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Error code.
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</p></td>
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</tr></tbody>
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</table></div>
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<p>
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Time complexity: usually O(1), but may depend on the type of the
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RNG.
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||
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||
</p>
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||
</div>
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||
<div class="section">
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||
<div class="titlepage"><div><div><h3 class="title">
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||
<a name="igraph_rng_bits"></a>3.4. <code class="function">igraph_rng_bits</code> — The number of random bits that a random number generator can produces in a single round.</h3></div></div></div>
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||
<a class="indexterm" name="id-1.9.4.5.2"></a><p>
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||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_int_t igraph_rng_bits(const igraph_rng_t* rng);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
The RNG.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The number of random bits that can be generated in a single round
|
||
with the RNG.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: O(1).
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_max"></a>3.5. <code class="function">igraph_rng_max</code> — The maximum possible integer for a random number generator.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.4.6.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_uint_t igraph_rng_max(const igraph_rng_t *rng);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Note that this number is only for informational purposes; it returns the
|
||
maximum possible integer that can be generated with the RNG with a single
|
||
call to its internals. It is derived directly from the number of random
|
||
<span class="emphasis"><em>bits</em></span> that the RNG can generate in a single round. When this is smaller
|
||
than what would be needed by other RNG functions like <a class="link" href="igraph-Random.html#igraph_rng_get_integer" title="4.2. igraph_rng_get_integer — Generate an integer random number from an interval."><code class="function">igraph_rng_get_integer()</code></a>,
|
||
igraph will call the RNG multiple times to generate more random bits.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
The RNG.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The largest possible integer that can be generated in a single round
|
||
with the RNG.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: O(1).
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_name"></a>3.6. <code class="function">igraph_rng_name</code> — The type of a random number generator.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.4.7.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
const char *igraph_rng_name(const igraph_rng_t *rng);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
The RNG.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The name of the type of the generator. Do not deallocate or
|
||
change the returned string.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: O(1).
|
||
|
||
</p>
|
||
</div>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||
<a name="generating-random-numbers"></a>4. Generating random numbers</h2></div></div></div>
|
||
<div class="toc"><dl class="toc">
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_bool">4.1. <code class="function">igraph_rng_get_bool</code> — Generate a random boolean.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_integer">4.2. <code class="function">igraph_rng_get_integer</code> — Generate an integer random number from an interval.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_unif01">4.3. <code class="function">igraph_rng_get_unif01</code> — Samples uniformly from the unit interval.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_unif">4.4. <code class="function">igraph_rng_get_unif</code> — Samples real numbers from a given interval.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_normal">4.5. <code class="function">igraph_rng_get_normal</code> — Samples from a normal distribution.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_exp">4.6. <code class="function">igraph_rng_get_exp</code> — Samples from an exponential distribution.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_gamma">4.7. <code class="function">igraph_rng_get_gamma</code> — Samples from a gamma distribution.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_binom">4.8. <code class="function">igraph_rng_get_binom</code> — Samples from a binomial distribution.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_geom">4.9. <code class="function">igraph_rng_get_geom</code> — Samples from a geometric distribution.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rng_get_pois">4.10. <code class="function">igraph_rng_get_pois</code> — Samples from a Poisson distribution.</a></span></dt>
|
||
</dl></div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_bool"></a>4.1. <code class="function">igraph_rng_get_bool</code> — Generate a random boolean.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.2.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_bool_t igraph_rng_get_bool(igraph_rng_t *rng);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Use this function only when a single random boolean, i.e. a single bit
|
||
is needed at a time. It is not efficient for generating multiple bits.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use for the generation. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a> here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated bit, as a truth value.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_integer"></a>4.2. <code class="function">igraph_rng_get_integer</code> — Generate an integer random number from an interval.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.3.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_int_t igraph_rng_get_integer(
|
||
igraph_rng_t *rng, igraph_int_t l, igraph_int_t h
|
||
);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generate uniformly distributed integers from the interval <code class="literal">[l, h]</code>.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use for the generation. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a> here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>l</code></em>:</span></p></td>
|
||
<td><p>
|
||
Lower limit, inclusive, it can be negative as well.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>h</code></em>:</span></p></td>
|
||
<td><p>
|
||
Upper limit, inclusive, it can be negative as well, but it
|
||
must be at least <code class="literal">l</code>.
|
||
</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated random integer.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: O(log2(h-l+1) / bits) where bits is the value of
|
||
<a class="link" href="igraph-Random.html#igraph_rng_bits" title="3.4. igraph_rng_bits — The number of random bits that a random number generator can produces in a single round."><code class="function">igraph_rng_bits</code></a>(rng).
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_unif01"></a>4.3. <code class="function">igraph_rng_get_unif01</code> — Samples uniformly from the unit interval.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.4.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_real_t igraph_rng_get_unif01(igraph_rng_t *rng);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generates uniformly distributed real numbers from the <code class="literal">[0, 1)</code>
|
||
half-open interval.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>
|
||
here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated uniformly distributed random number.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: depends on the type of the RNG.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_unif"></a>4.4. <code class="function">igraph_rng_get_unif</code> — Samples real numbers from a given interval.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.5.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_real_t igraph_rng_get_unif(igraph_rng_t *rng,
|
||
igraph_real_t l, igraph_real_t h);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generates uniformly distributed real numbers from the <code class="literal">[l, h)</code>
|
||
half-open interval.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>
|
||
here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>l</code></em>:</span></p></td>
|
||
<td><p>
|
||
The lower bound, it can be negative.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>h</code></em>:</span></p></td>
|
||
<td><p>
|
||
The upper bound, it can be negative, but it has to be
|
||
larger than the lower bound.
|
||
</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated uniformly distributed random number.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: depends on the type of the RNG.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_normal"></a>4.5. <code class="function">igraph_rng_get_normal</code> — Samples from a normal distribution.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.6.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_real_t igraph_rng_get_normal(igraph_rng_t *rng,
|
||
igraph_real_t m, igraph_real_t s);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generates random variates from a normal distribution with probability
|
||
density
|
||
|
||
</p>
|
||
<p>
|
||
<code class="literal">exp( -(x - m)^2 / (2 s^2) )</code>.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>
|
||
here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>m</code></em>:</span></p></td>
|
||
<td><p>
|
||
The mean.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>s</code></em>:</span></p></td>
|
||
<td><p>
|
||
The standard deviation.
|
||
</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated normally distributed random number.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: depends on the type of the RNG.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_exp"></a>4.6. <code class="function">igraph_rng_get_exp</code> — Samples from an exponential distribution.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.7.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_real_t igraph_rng_get_exp(igraph_rng_t *rng, igraph_real_t rate);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generates random variates from an exponential distribution with probability
|
||
density proportional to
|
||
|
||
</p>
|
||
<p>
|
||
<code class="literal">exp(-rate x)</code>.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>
|
||
here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rate</code></em>:</span></p></td>
|
||
<td><p>
|
||
Rate parameter.
|
||
</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated sample.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: depends on the RNG.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_gamma"></a>4.7. <code class="function">igraph_rng_get_gamma</code> — Samples from a gamma distribution.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.8.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_real_t igraph_rng_get_gamma(igraph_rng_t *rng, igraph_real_t shape,
|
||
igraph_real_t scale);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generates random variates from a gamma distribution with probability
|
||
density proportional to
|
||
|
||
</p>
|
||
<p>
|
||
<code class="literal">x^(shape-1) exp(-x / scale)</code>.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>
|
||
here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>shape</code></em>:</span></p></td>
|
||
<td><p>
|
||
Shape parameter.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>scale</code></em>:</span></p></td>
|
||
<td><p>
|
||
Scale parameter.
|
||
</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated sample.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: depends on the RNG.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_binom"></a>4.8. <code class="function">igraph_rng_get_binom</code> — Samples from a binomial distribution.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.9.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_real_t igraph_rng_get_binom(igraph_rng_t *rng, igraph_int_t n, igraph_real_t p);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generates random variates from a binomial distribution. The number <code class="constant">k</code> is generated
|
||
with probability
|
||
|
||
</p>
|
||
<p>
|
||
<code class="literal">(n \choose k) p^k (1-p)^(n-k)</code>, <code class="literal">k = 0, 1, ..., n</code>.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>
|
||
here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>n</code></em>:</span></p></td>
|
||
<td><p>
|
||
Number of observations.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>p</code></em>:</span></p></td>
|
||
<td><p>
|
||
Probability of an event.
|
||
</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated binomially distributed random number.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: depends on the RNG.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_geom"></a>4.9. <code class="function">igraph_rng_get_geom</code> — Samples from a geometric distribution.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.10.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_real_t igraph_rng_get_geom(igraph_rng_t *rng, igraph_real_t p);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generates random variates from a geometric distribution. The number <code class="constant">k</code> is
|
||
generated with probability
|
||
|
||
</p>
|
||
<p>
|
||
<code class="literal">(1 - p)^k p</code>, <code class="literal">k = 0, 1, 2, ...</code>.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>
|
||
here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>p</code></em>:</span></p></td>
|
||
<td><p>
|
||
The probability of success in each trial. Must be larger
|
||
than zero and smaller or equal to 1.
|
||
</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated geometrically distributed random number.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: depends on the RNG.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rng_get_pois"></a>4.10. <code class="function">igraph_rng_get_pois</code> — Samples from a Poisson distribution.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.5.11.2"></a><p>
|
||
</p>
|
||
<div class="informalexample"><pre class="programlisting">
|
||
igraph_real_t igraph_rng_get_pois(igraph_rng_t *rng, igraph_real_t rate);
|
||
</pre></div>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
|
||
Generates random variates from a Poisson distribution. The number <code class="constant">k</code> is generated
|
||
with probability
|
||
|
||
</p>
|
||
<p>
|
||
<code class="literal">rate^k * exp(-rate) / k!</code>, <code class="literal">k = 0, 1, 2, ...</code>.
|
||
|
||
</p>
|
||
<p><b>Arguments: </b>
|
||
</p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rng</code></em>:</span></p></td>
|
||
<td><p>
|
||
Pointer to the RNG to use. Use <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>
|
||
here to use the default igraph RNG.
|
||
</p></td>
|
||
</tr>
|
||
<tr>
|
||
<td><p><span class="term"><em class="parameter"><code>rate</code></em>:</span></p></td>
|
||
<td><p>
|
||
The rate parameter of the Poisson distribution. Must not be negative.
|
||
</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table></div>
|
||
<p>
|
||
</p>
|
||
<p><b>Returns: </b></p>
|
||
<div class="variablelist"><table border="0" class="variablelist">
|
||
<colgroup>
|
||
<col align="left" valign="top">
|
||
<col>
|
||
</colgroup>
|
||
<tbody><tr>
|
||
<td><p><span class="term"><em class="parameter"><code></code></em></span></p></td>
|
||
<td><p>
|
||
The generated geometrically distributed random number.
|
||
</p></td>
|
||
</tr></tbody>
|
||
</table></div>
|
||
<p>
|
||
|
||
Time complexity: depends on the RNG.
|
||
|
||
</p>
|
||
</div>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||
<a name="supported-random-number-generators"></a>5. Supported random number generators</h2></div></div></div>
|
||
<div class="toc"><dl class="toc">
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rngtype_mt19937">5.1. <code class="function">igraph_rngtype_mt19937</code> — The MT19937 random number generator.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rngtype_glibc2">5.2. <code class="function">igraph_rngtype_glibc2</code> — The random number generator introduced in GNU libc 2.</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rngtype_pcg32">5.3. <code class="function">igraph_rngtype_pcg32</code> — The PCG random number generator (32-bit version).</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#igraph_rngtype_pcg64">5.4. <code class="function">igraph_rngtype_pcg64</code> — The PCG random number generator (64-bit version).</a></span></dt>
|
||
</dl></div>
|
||
<p>
|
||
By default igraph uses the MT19937 generator. Prior to igraph version
|
||
0.6, the generator supplied by the standard C library was used. This
|
||
means the GLIBC2 generator on GNU libc 2 systems, and maybe the BSD RAND
|
||
generator on others. The RAND generator was removed due to poor statistical
|
||
properties in version 0.10. The PCG32 generator was added in version 0.10.
|
||
</p>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rngtype_mt19937"></a>5.1. <code class="function">igraph_rngtype_mt19937</code> — The MT19937 random number generator.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.6.3.2"></a><p>
|
||
</p>
|
||
<pre class="programlisting">
|
||
const igraph_rng_type_t igraph_rngtype_mt19937 = {
|
||
/* name= */ "MT19937",
|
||
/* bits= */ 32,
|
||
/* init= */ igraph_rng_mt19937_init,
|
||
/* destroy= */ igraph_rng_mt19937_destroy,
|
||
/* seed= */ igraph_rng_mt19937_seed,
|
||
/* get= */ igraph_rng_mt19937_get,
|
||
/* get_int= */ NULL,
|
||
/* get_real= */ NULL,
|
||
/* get_norm= */ NULL,
|
||
/* get_geom= */ NULL,
|
||
/* get_binom= */ NULL,
|
||
/* get_exp= */ NULL,
|
||
/* get_gamma= */ NULL,
|
||
/* get_pois= */ NULL
|
||
};
|
||
</pre>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
The MT19937 generator of Makoto Matsumoto and Takuji Nishimura is a
|
||
variant of the twisted generalized feedback shift-register
|
||
algorithm, and is known as the “Mersenne Twister” generator. It has
|
||
a Mersenne prime period of 2^19937 - 1 (about 10^6000) and is
|
||
equi-distributed in 623 dimensions. It has passed the diehard
|
||
statistical tests. It uses 624 words of state per generator and is
|
||
comparable in speed to the other generators. The original generator
|
||
used a default seed of 4357 and choosing <code class="constant">s</code> equal to zero in
|
||
<code class="constant">igraph_rng_mt19937_seed</code>() reproduces this. Later versions switched to
|
||
5489 as the default seed, you can choose this explicitly via
|
||
<a class="link" href="igraph-Random.html#igraph_rng_seed" title="3.3. igraph_rng_seed — Seeds a random number generator."><code class="function">igraph_rng_seed()</code></a> instead if you require it.
|
||
|
||
</p>
|
||
<p>
|
||
For more information see,
|
||
Makoto Matsumoto and Takuji Nishimura, “Mersenne Twister: A
|
||
623-dimensionally equidistributed uniform pseudorandom number
|
||
generator”. ACM Transactions on Modeling and Computer Simulation,
|
||
Vol. 8, No. 1 (Jan. 1998), Pages 3–30
|
||
|
||
</p>
|
||
<p>
|
||
The generator <code class="constant">igraph_rngtype_mt19937</code> uses the second revision of the
|
||
seeding procedure published by the two authors above in 2002. The
|
||
original seeding procedures could cause spurious artifacts for some
|
||
seed values.
|
||
|
||
</p>
|
||
<p>
|
||
This generator was ported from the GNU Scientific Library.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rngtype_glibc2"></a>5.2. <code class="function">igraph_rngtype_glibc2</code> — The random number generator introduced in GNU libc 2.</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.6.4.2"></a><p>
|
||
</p>
|
||
<pre class="programlisting">
|
||
const igraph_rng_type_t igraph_rngtype_glibc2 = {
|
||
/* name= */ "LIBC",
|
||
/* bits= */ 31,
|
||
/* init= */ igraph_rng_glibc2_init,
|
||
/* destroy= */ igraph_rng_glibc2_destroy,
|
||
/* seed= */ igraph_rng_glibc2_seed,
|
||
/* get= */ igraph_rng_glibc2_get,
|
||
/* get_int= */ NULL,
|
||
/* get_real= */ NULL,
|
||
/* get_norm= */ NULL,
|
||
/* get_geom= */ NULL,
|
||
/* get_binom= */ NULL,
|
||
/* get_exp= */ NULL,
|
||
/* get_gamma= */ NULL,
|
||
/* get_pois= */ NULL
|
||
};
|
||
</pre>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
This is a linear feedback shift register generator with a 128-byte
|
||
buffer. This generator was the default prior to igraph version 0.6,
|
||
at least on systems relying on GNU libc.
|
||
|
||
This generator was ported from the GNU Scientific Library. It is a
|
||
reimplementation and does not call the system glibc generator.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rngtype_pcg32"></a>5.3. <code class="function">igraph_rngtype_pcg32</code> — The PCG random number generator (32-bit version).</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.6.5.2"></a><p>
|
||
</p>
|
||
<pre class="programlisting">
|
||
const igraph_rng_type_t igraph_rngtype_pcg32 = {
|
||
/* name= */ "PCG32",
|
||
/* bits= */ 32,
|
||
/* init= */ igraph_rng_pcg32_init,
|
||
/* destroy= */ igraph_rng_pcg32_destroy,
|
||
/* seed= */ igraph_rng_pcg32_seed,
|
||
/* get= */ igraph_rng_pcg32_get,
|
||
/* get_int= */ NULL,
|
||
/* get_real= */ NULL,
|
||
/* get_norm= */ NULL,
|
||
/* get_geom= */ NULL,
|
||
/* get_binom= */ NULL,
|
||
/* get_exp= */ NULL,
|
||
/* get_gamma= */ NULL,
|
||
/* get_pois= */ NULL
|
||
};
|
||
</pre>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
This is an implementation of the PCG random number generator; see
|
||
<a class="ulink" href="https://www.pcg-random.org" target="_top">https://www.pcg-random.org</a> for more details. This implementation returns
|
||
32 random bits in a single iteration.
|
||
|
||
</p>
|
||
<p>
|
||
The generator was ported from the original source code published by the
|
||
authors at <a class="ulink" href="https://github.com/imneme/pcg-c" target="_top">https://github.com/imneme/pcg-c</a>.
|
||
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="igraph_rngtype_pcg64"></a>5.4. <code class="function">igraph_rngtype_pcg64</code> — The PCG random number generator (64-bit version).</h3></div></div></div>
|
||
<a class="indexterm" name="id-1.9.6.6.2"></a><p>
|
||
</p>
|
||
<pre class="programlisting">
|
||
const igraph_rng_type_t igraph_rngtype_pcg64 = {
|
||
/* name= */ "PCG64",
|
||
/* bits= */ 64,
|
||
/* init= */ igraph_rng_pcg64_init,
|
||
/* destroy= */ igraph_rng_pcg64_destroy,
|
||
/* seed= */ igraph_rng_pcg64_seed,
|
||
/* get= */ igraph_rng_pcg64_get,
|
||
/* get_int= */ NULL,
|
||
/* get_real= */ NULL,
|
||
/* get_norm= */ NULL,
|
||
/* get_geom= */ NULL,
|
||
/* get_binom= */ NULL,
|
||
/* get_exp= */ NULL,
|
||
/* get_gamma= */ NULL,
|
||
/* get_pois= */ NULL
|
||
};
|
||
</pre>
|
||
<p>
|
||
</p>
|
||
<p>
|
||
|
||
|
||
This is an implementation of the PCG random number generator; see
|
||
<a class="ulink" href="https://www.pcg-random.org" target="_top">https://www.pcg-random.org</a> for more details. This implementation returns
|
||
64 random bits in a single iteration. It is only available on 64-bit plaforms
|
||
with compilers that provide the __uint128_t type.
|
||
|
||
</p>
|
||
<p>
|
||
PCG64 typically provides better performance than PCG32 when sampling floating
|
||
point numbers or very large integers, as it can provide twice as many random
|
||
bits in a single generation round.
|
||
|
||
</p>
|
||
<p>
|
||
The generator was ported from the original source code published by the
|
||
authors at <a class="ulink" href="https://github.com/imneme/pcg-c" target="_top">https://github.com/imneme/pcg-c</a>.
|
||
|
||
</p>
|
||
</div>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
|
||
<a name="random-use-cases"></a>6. Use cases</h2></div></div></div>
|
||
<div class="toc"><dl class="toc">
|
||
<dt><span class="section"><a href="igraph-Random.html#random-normal-use">6.1. Normal (default) use</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#random-reproducible-simulations">6.2. Reproducible simulations</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#random-changing-default-generator">6.3. Changing the default generator</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#random-using-multiple-generators">6.4. Using multiple generators</a></span></dt>
|
||
<dt><span class="section"><a href="igraph-Random.html#random-example">6.5. Example</a></span></dt>
|
||
</dl></div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="random-normal-use"></a>6.1. Normal (default) use</h3></div></div></div>
|
||
<p>
|
||
If the user does not use any of the RNG functions explicitly, but calls
|
||
some of the randomized igraph functions, then a default RNG is set
|
||
up the first time an igraph function needs random numbers. The
|
||
seed of this RNG is the output of the <code class="literal">time(0)</code> function
|
||
call, using the <code class="literal">time</code> function from the standard C
|
||
library. This ensures that igraph creates a different random graph,
|
||
each time the C program is called.
|
||
</p>
|
||
<p>
|
||
The created default generator is stored internally and can be
|
||
queried with the <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a> function.
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="random-reproducible-simulations"></a>6.2. Reproducible simulations</h3></div></div></div>
|
||
<p>
|
||
If reproducible results are needed, then the user should set the
|
||
seed of the default random number generator explicitly, using the
|
||
<a class="link" href="igraph-Random.html#igraph_rng_seed" title="3.3. igraph_rng_seed — Seeds a random number generator."><code class="function">igraph_rng_seed()</code></a> function on the default generator, <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a>. When setting the seed to the same number,
|
||
igraph generates exactly the same random graph (or series of random
|
||
graphs).
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="random-changing-default-generator"></a>6.3. Changing the default generator</h3></div></div></div>
|
||
<p>
|
||
By default igraph uses the <a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator."><code class="function">igraph_rng_default()</code></a> random number
|
||
generator. This can be changed any time by calling <a class="link" href="igraph-Random.html#igraph_rng_set_default" title="2.2. igraph_rng_set_default — Set the default igraph random number generator."><code class="function">igraph_rng_set_default()</code></a>, with an already initialized random number
|
||
generator. Note that the old (replaced) generator is not
|
||
destroyed, so no memory is deallocated.
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="random-using-multiple-generators"></a>6.4. Using multiple generators</h3></div></div></div>
|
||
<p>
|
||
igraph also provides functions to set up multiple random number
|
||
generators, using the <a class="link" href="igraph-Random.html#igraph_rng_init" title="3.1. igraph_rng_init — Initializes a random number generator."><code class="function">igraph_rng_init()</code></a> function, and then
|
||
generating random numbers from them, e.g. with <a class="link" href="igraph-Random.html#igraph_rng_get_integer" title="4.2. igraph_rng_get_integer — Generate an integer random number from an interval."><code class="function">igraph_rng_get_integer()</code></a>
|
||
and/or <a class="link" href="igraph-Random.html#igraph_rng_get_unif" title="4.4. igraph_rng_get_unif — Samples real numbers from a given interval."><code class="function">igraph_rng_get_unif()</code></a> calls.
|
||
</p>
|
||
<p>
|
||
Note that initializing a new random number generator is
|
||
independent of the generator that the igraph functions themselves
|
||
use. If you want to replace that, then please use <a class="link" href="igraph-Random.html#igraph_rng_set_default" title="2.2. igraph_rng_set_default — Set the default igraph random number generator."><code class="function">igraph_rng_set_default()</code></a>.
|
||
</p>
|
||
</div>
|
||
<div class="section">
|
||
<div class="titlepage"><div><div><h3 class="title">
|
||
<a name="random-example"></a>6.5. Example</h3></div></div></div>
|
||
<p>
|
||
</p>
|
||
<div class="hideshow" onClick="toggle(this, event)">
|
||
<div class="example">
|
||
<a name="id-1.9.7.6.2.1"></a><p class="title"><b>Example 8.1. File <code class="code">examples/simple/random_seed.c</code></b></p>
|
||
<div class="example-contents">
|
||
<pre class="programlisting"><span class="strong"><strong>#include</strong></span> <igraph.h>
|
||
|
||
int <span class="strong"><strong>main</strong></span>(void) {
|
||
igraph_t g1, g2;
|
||
igraph_bool_t iso;
|
||
|
||
<span class="emphasis"><em>/* Initialize the library. */</em></span>
|
||
<span class="strong"><strong><a class="link" href="igraph-Basic.html#igraph_setup" title="4.1. igraph_setup — Initializes the igraph library.">igraph_setup</a></strong></span>();
|
||
|
||
<span class="emphasis"><em>/* Seed the default random number generator and create a random graph. */</em></span>
|
||
<span class="strong"><strong><a class="link" href="igraph-Random.html#igraph_rng_seed" title="3.3. igraph_rng_seed — Seeds a random number generator.">igraph_rng_seed</a></strong></span>(<span class="strong"><strong><a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator.">igraph_rng_default</a></strong></span>(), 1122);
|
||
|
||
<span class="strong"><strong><a class="link" href="igraph-Games.html#igraph_erdos_renyi_game_gnp" title="1.2. igraph_erdos_renyi_game_gnp — Generates a random (Erdős-Rényi) graph with fixed edge probabilities.">igraph_erdos_renyi_game_gnp</a></strong></span>(&g1, 100, 3.0 / 100, IGRAPH_UNDIRECTED, IGRAPH_SIMPLE_SW, IGRAPH_EDGE_UNLABELED);
|
||
|
||
<span class="emphasis"><em>/* Seed the generator with the same seed again,</em></span>
|
||
<span class="emphasis"><em> * and create a graph with the same method. */</em></span>
|
||
|
||
<span class="strong"><strong><a class="link" href="igraph-Random.html#igraph_rng_seed" title="3.3. igraph_rng_seed — Seeds a random number generator.">igraph_rng_seed</a></strong></span>(<span class="strong"><strong><a class="link" href="igraph-Random.html#igraph_rng_default" title="2.1. igraph_rng_default — Query the default random number generator.">igraph_rng_default</a></strong></span>(), 1122);
|
||
|
||
<span class="strong"><strong><a class="link" href="igraph-Games.html#igraph_erdos_renyi_game_gnp" title="1.2. igraph_erdos_renyi_game_gnp — Generates a random (Erdős-Rényi) graph with fixed edge probabilities.">igraph_erdos_renyi_game_gnp</a></strong></span>(&g2, 100, 3.0 / 100, IGRAPH_UNDIRECTED, IGRAPH_SIMPLE_SW, IGRAPH_EDGE_UNLABELED);
|
||
|
||
<span class="emphasis"><em>/* The two graphs will be identical. */</em></span>
|
||
|
||
<span class="strong"><strong><a class="link" href="igraph-Basic.html#igraph_is_same_graph" title="6.6. igraph_is_same_graph — Are two graphs identical as labelled graphs?">igraph_is_same_graph</a></strong></span>(&g1, &g2, &iso);
|
||
|
||
<span class="strong"><strong>if</strong></span> (!iso) {
|
||
<span class="strong"><strong>return</strong></span> 1;
|
||
}
|
||
|
||
<span class="emphasis"><em>/* Destroy no longer needed data structures. */</em></span>
|
||
|
||
<span class="strong"><strong><a class="link" href="igraph-Basic.html#igraph_destroy" title="5.1.4. igraph_destroy — Frees the memory allocated for a graph object.">igraph_destroy</a></strong></span>(&g2);
|
||
<span class="strong"><strong><a class="link" href="igraph-Basic.html#igraph_destroy" title="5.1.4. igraph_destroy — Frees the memory allocated for a graph object.">igraph_destroy</a></strong></span>(&g1);
|
||
|
||
<span class="strong"><strong>return</strong></span> 0;
|
||
}
|
||
</pre>
|
||
<p></p>
|
||
</div>
|
||
</div>
|
||
<br class="example-break">
|
||
</div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<table class="navigation-footer" width="100%" summary="Navigation footer" cellpadding="2" cellspacing="0"><tr valign="middle">
|
||
<td align="left"><a accesskey="p" href="igraph-Data-structures.html"><b>← Chapter 7. Data structure library: vector, matrix, other data types</b></a></td>
|
||
<td align="right"><a accesskey="n" href="igraph-Iterators.html"><b>Chapter 9. Vertex and edge selectors and sequences, iterators →</b></a></td>
|
||
</tr></table>
|
||
</body>
|
||
</html>
|