ters for) nodes 1 and 2 are not tied to
subsequent slices.
<p>
Above we assumed the observation model P(Y(t) | X(t)) is independent of t for t>1, but
it is conventional to assume this is true for all t.
So we would like to put nodes 2, 4, 6, ... all in the same class.
We can do this by explicitely defining the equivalence classes, as
follows (see <a href="usage.html#tying">here</a> for more details on
parameter tying).
<p>
We define eclass1(i) to be the equivalence class that node i in slice
1 belongs to.
S