I'm writing an AI for a card game and after some testing I've discovered that using MTD(f) on my alpha beta algorithm - a series of zero-window searches - is faster than just using alpha-beta by itself.
The MTD(f) algorithm is described well here http://people.csail.mit.edu/plaat/mtdf.html
The problem I have is that for each pass in the MTD(f) search (for each guess) I don't reuse any of the previous positions I have stored even though the write up on the link suggests that I should (in fact clearing the table between iterations speeds up the algorithm).
My problem is that when I store a position and a value in my transposition table I also store the alpha and beta values for which it is valid. Therefore a second pass through the tree with a different guess (and therefore alpha and beta) can't possibly reuse any information. Is this what is to be expected or am I missing something fundamental here?
For instance if for alpha=3 beta=4 we come to a result of 7 (obviously a cut-off) should I store that in the table as valid for alpha=3 to beta=6? Or beta=7?