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<h3 class="section">21.12 Two dimensional histograms</h3>
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<p><a name="index-two-dimensional-histograms-1806"></a><a name="index-g_t2D-histograms-1807"></a>
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A two dimensional histogram consists of a set of <dfn>bins</dfn> which count
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the number of events falling in a given area of the (x,y)
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plane. The simplest way to use a two dimensional histogram is to record
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two-dimensional position information, n(x,y). Another possibility
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is to form a <dfn>joint distribution</dfn> by recording related
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variables. For example a detector might record both the position of an
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event (x) and the amount of energy it deposited E. These
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could be histogrammed as the joint distribution n(x,E).