m class="sig-param"><span class="n"><span class="pre">nw</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#utils.qiinv" title="Permalink to this definition">¶</a></dt>
<dd><p>Function to calculate the Quadratic Spectrum using the method 
developed by Prieto et al. (2007).</p>
<p>The first 2 derivatives of the spectrum are estimated and the 
bias associated with curvature (2nd derivative) is reduced.</p>
<p>Calculate the Stationary Inverse Theory Spectrum.
Basically, compute the