[Ligncse256] Iterating through states in the trellis

[Dan Kleinman]

Hi Everyone,

In building the decoder, I'm having trouble trying to figure out a 
not-terribly-inefficient way to iterate through all of the states in the 
trellis, which is necessary to calculate state weights and add 
backpointers. I can see that the states in the trellis are related 
through forwardTransitions/backwardTransitions, which, if we assume that 
every state in a given position is connected to every state in the next 
position, makes this process relatively easy - the model could access 
all of the forward transitions from states in a given position by 
looking at the backward transitions from all states forward of any node 
in that position. The problem is, after sprinkling some Print statements 
throughout my code, I'm not convinced that that assumption - that 
everything is connected - is valid: the number of backwardTransitions my 
trellis uses is different from how many I would expect there to be if 
that were the case (i.e., the sum of the products of the number of 
states at every two consecutive positions). Is my math screwy, or is 
there a better way to implement the iteration?

Thanks,
Dan Kleinman