imilarly, we define eclass2(i) to be the equivalence class that node i in slice
2, 3, ..., belongs to.
For an HMM, we have
<pre>
eclass1 = [1 2];
eclass2 = [3 2];
eclass = [eclass1 eclass2];
</pre>
This ties the observation model across slices,
since e.g., eclass(4) = eclass(2) = 2.
<p>
By default,
eclass1 = 1:ss, and eclass2 = (1:ss)+ss, where ss = slice size = the
number of nodes per slice.
<!--This will tie nodes in slices 3, 4, ... to the the nodes in slice 2,
but none of the nodes in slice 2 to any in 