span class="sd">                it is assumed that y=x.</span>

<span class="sd">        Returns:</span>
<span class="sd">            The pairwise global similarity kernel K[i,j] between the given</span>
<span class="sd">            structures, in the same order as given in the input, i.e. the</span>
<span class="sd">            similarity of structures i and j is given by K[i,j], where features</span>
<span class="sd">            for structure i and j were in features[i] and features[j]</span>
<span class=