erwise 0.
 <p>
 The least squares estimate of the intercept is computed using the
 <a href="http://www.xycoon.com/estimation4.htm">normal equations</a>.
 The intercept is sometimes denoted b0.</p>
 <p>
 <strong>Preconditions</strong>: <ul>
 <li>At least two observations (with at least two different x values)
 must have been added before invoking this method. If this method is
 invoked before a model can be estimated, <code>Double,NaN</code> is
 returned.
 </li></ul></p></div>
<dl><dt><span class="strong">Re