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<title>GNU Scientific Library – Reference Manual: N-tuples</title>
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Next: <a href="Monte-Carlo-Integration.html#Monte-Carlo-Integration" accesskey="n" rel="next">Monte Carlo Integration</a>, Previous: <a href="Histograms.html#Histograms" accesskey="p" rel="previous">Histograms</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<a name="N_002dtuples-1"></a>
<h2 class="chapter">23 N-tuples</h2>
<a name="index-ntuples"></a>
<p>This chapter describes functions for creating and manipulating
<em>ntuples</em>, sets of values associated with events. The ntuples
are stored in files. Their values can be extracted in any combination
and <em>booked</em> in a histogram using a selection function.
</p>
<p>The values to be stored are held in a user-defined data structure, and
an ntuple is created associating this data structure with a file. The
values are then written to the file (normally inside a loop) using
the ntuple functions described below.
</p>
<p>A histogram can be created from ntuple data by providing a selection
function and a value function. The selection function specifies whether
an event should be included in the subset to be analyzed or not. The value
function computes the entry to be added to the histogram for each
event.
</p>
<p>All the ntuple functions are defined in the header file
<samp>gsl_ntuple.h</samp>
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">• <a href="The-ntuple-struct.html#The-ntuple-struct" accesskey="1">The ntuple struct</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Creating-ntuples.html#Creating-ntuples" accesskey="2">Creating ntuples</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Opening-an-existing-ntuple-file.html#Opening-an-existing-ntuple-file" accesskey="3">Opening an existing ntuple file</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Writing-ntuples.html#Writing-ntuples" accesskey="4">Writing ntuples</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Reading-ntuples.html#Reading-ntuples" accesskey="5">Reading ntuples </a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Closing-an-ntuple-file.html#Closing-an-ntuple-file" accesskey="6">Closing an ntuple file</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Histogramming-ntuple-values.html#Histogramming-ntuple-values" accesskey="7">Histogramming ntuple values</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Example-ntuple-programs.html#Example-ntuple-programs" accesskey="8">Example ntuple programs</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Ntuple-References-and-Further-Reading.html#Ntuple-References-and-Further-Reading" accesskey="9">Ntuple References and Further Reading</a>:</td><td> </td><td align="left" valign="top">
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