his method. If this method is
 invoked before a model can be estimated, <code>Double.NaN</code> is
 returned.
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<dl><dt><span class="strong">Returns:</span></dt><dd>sum of squared deviations of predicted y values</dd></dl>
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<h4>getMeanSquareError</h4>
<pre>public&nbsp;double&nbsp;getMeanSquareError()</pre>
<div class="block">Returns the sum of squared errors divided by the degrees of 