from the regression data set.
 <p>
 Mirrors the addData method.  This method permits the use of
 SimpleRegression instances in streaming mode where the regression
 is applied to a sliding "window" of observations, however the caller is
 responsible for maintaining the set of observations in the window.</p>

 The method has no effect if there are no points of data (i.e. n=0)</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>x</code> - independent variable value</dd><dd><code>y</code> - depe