the equivalence class that node i in slice
2, 3, ..., belongs to.
For the water model, we have
<pre>
</pre>
This ties the observation model across slices,
since e.g., eclass(9) = eclass(21) = 9, so Y(1,1) and Y(1,2) belong to the
same class.
<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 slice 1.
By using the above tieing pattern,
we