What does this excerpt of c++ mean?
<p>I'm simply trying to understand what is being reffered to by <code>dX()</code> or <code>dY()</code> in</p>

<pre><code>Table2D&lt;double&gt; grad2(const Table2D&lt;double&gt;&amp; intensity) {
    return grad2(intensity, dX(), dY());
}

Table2D&lt;double&gt; grad2(
    const Table2D&lt;double&gt;&amp; intensity,
    const Kernel2D&lt;double&gt;&amp; dX,
    const Kernel2D&lt;double&gt;&amp; dY)
{
    Assert(
      dX.getWidth() &lt;= intensity.getWidth()
   &amp;&amp; dX.getHeight() &lt;= intensity.getHeight(),
      "kernel 'dX' is bigger than array 'intensity' (in grad2)");
    Assert(!dX.isEmpty(), "kernel 'dX' is empty (in grad2)");  

    Table2D&lt;double&gt; Ix(intensity*dX), Iy(intensity*dY);
    return ((Ix%=Ix)+=(Iy%=Iy));
}
</code></pre>

<p>I have searched the document up and down with all sorts of settings in the finder window (case sensetive etc...) and I couldn't find a function with the name <code>dX()</code> or <code>dY()</code> anywhere. no namespace is being used either so it would have to reference something in the same document right?</p>
