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<a name="Histogram-allocation"></a>
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<p>
Next: <a href="Copying-Histograms.html#Copying-Histograms" accesskey="n" rel="next">Copying Histograms</a>, Previous: <a href="The-histogram-struct.html#The-histogram-struct" accesskey="p" rel="previous">The histogram struct</a>, Up: <a href="Histograms.html#Histograms" accesskey="u" rel="up">Histograms</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Histogram-allocation-1"></a>
<h3 class="section">23.2 Histogram allocation</h3>
<p>The functions for allocating memory to a histogram follow the style of
<code>malloc</code> and <code>free</code>. In addition they also perform their own
error checking. If there is insufficient memory available to allocate a
histogram then the functions call the error handler (with an error
number of <code>GSL_ENOMEM</code>) in addition to returning a null pointer.
Thus if you use the library error handler to abort your program then it
isn’t necessary to check every histogram <code>alloc</code>.
</p>
<dl>
<dt><a name="index-gsl_005fhistogram_005falloc"></a>Function: <em>gsl_histogram *</em> <strong>gsl_histogram_alloc</strong> <em>(size_t <var>n</var>)</em></dt>
<dd><p>This function allocates memory for a histogram with <var>n</var> bins, and
returns a pointer to a newly created <code>gsl_histogram</code> struct. If
insufficient memory is available a null pointer is returned and the
error handler is invoked with an error code of <code>GSL_ENOMEM</code>. The
bins and ranges are not initialized, and should be prepared using one of
the range-setting functions below in order to make the histogram ready
for use.
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005fhistogram_005fset_005franges"></a>Function: <em>int</em> <strong>gsl_histogram_set_ranges</strong> <em>(gsl_histogram * <var>h</var>, const double <var>range</var>[], size_t <var>size</var>)</em></dt>
<dd><p>This function sets the ranges of the existing histogram <var>h</var> using
the array <var>range</var> of size <var>size</var>. The values of the histogram
bins are reset to zero. The <code>range</code> array should contain the
desired bin limits. The ranges can be arbitrary, subject to the
restriction that they are monotonically increasing.
</p>
<p>The following example shows how to create a histogram with logarithmic
bins with ranges [1,10), [10,100) and [100,1000).
</p>
<div class="example">
<pre class="example">gsl_histogram * h = gsl_histogram_alloc (3);
/* bin[0] covers the range 1 <= x < 10 */
/* bin[1] covers the range 10 <= x < 100 */
/* bin[2] covers the range 100 <= x < 1000 */
double range[4] = { 1.0, 10.0, 100.0, 1000.0 };
gsl_histogram_set_ranges (h, range, 4);
</pre></div>
<p>Note that the size of the <var>range</var> array should be defined to be one
element bigger than the number of bins. The additional element is
required for the upper value of the final bin.
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005fhistogram_005fset_005franges_005funiform"></a>Function: <em>int</em> <strong>gsl_histogram_set_ranges_uniform</strong> <em>(gsl_histogram * <var>h</var>, double <var>xmin</var>, double <var>xmax</var>)</em></dt>
<dd><p>This function sets the ranges of the existing histogram <var>h</var> to cover
the range <var>xmin</var> to <var>xmax</var> uniformly. The values of the
histogram bins are reset to zero. The bin ranges are shown in the table
below,
</p><div class="display">
<pre class="display">bin[0] corresponds to xmin <= x < xmin + d
bin[1] corresponds to xmin + d <= x < xmin + 2 d
......
bin[n-1] corresponds to xmin + (n-1)d <= x < xmax
</pre></div>
<p>where <em>d</em> is the bin spacing, <em>d = (xmax-xmin)/n</em>.
</p></dd></dl>
<dl>
<dt><a name="index-gsl_005fhistogram_005ffree"></a>Function: <em>void</em> <strong>gsl_histogram_free</strong> <em>(gsl_histogram * <var>h</var>)</em></dt>
<dd><p>This function frees the histogram <var>h</var> and all of the memory
associated with it.
</p></dd></dl>
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