in selection method for distance distribution, either
an integer &gt; 1 indicating the number of bins, or one of the following strings 
{<code class="docutils literal notranslate"><span class="pre">'sturges'</span></code>, <code class="docutils literal notranslate"><span class="pre">'sqrt'</span></code>, <code class="docutils literal notranslate"><span class="pre">'rice'</span></code>, <code class="docutils literal notranslate"><span class="pre">'doanes'</span></code>} [default: <code class="docutils litera