I spectrum estimate</p>
</dd>
<dt>ds<span class="classifier">ndarray [nfft,0]       </span></dt><dd><p>the estimate of the first derivative</p>
</dd>
<dt>dds<span class="classifier">ndarray [nfft,0]      </span></dt><dd><p>the estimate of the second derivative</p>
</dd>
</dl>
<p><strong>References</strong></p>
<p>G. A. Prieto, R. L. Parker, D. J. Thomson, F. L. Vernon, 
and R. L. Graham (2007), Reducing the bias of multitaper 
spectrum estimates,  Geophys. J. Int., 171, 1269-1281. 
doi: 10.1111/j.1365-246X.