lass="keywordtype">size_t</span> i, <span class="keywordtype">size_t</span> j) <span class="keyword">const</span> = 0;
<a name="l00255"></a>00255 
<a name="l00256"></a>00256   <span class="comment">// return forward log-prob of the j-th tag at i-th token</span>
<a name="l00257"></a>00257   <span class="keyword">virtual</span> <span class="keywordtype">double</span> alpha(<span class="keywordtype">size_t</span> i, <span class="keywordtype">size_t</span> j) <span class="keyword">const</span> = 0;
<a name="l00