Iterative deepening with a time limit

Question

I'm working on implementing iterative deepening with principal variation for alpha-beta search for a computer chess program, and I was hoping to include a time limit for the search. I was wondering about the consequences of the time limit being reached in the middle of, say, a search at a depth of 5. If this incomplete search has found a new principal variation, would that be guaranteed to be at least as good as the principal variation found by the complete search at a depth of 4? Otherwise, it seems like I should throw out anything found by the incomplete search at a depth of 5.

Answer 1

If you stop in the middle of an iteration you can use the best move found so far backed up to the root on that iteration. It's not guaranteed to be at least as good as the best move found by the previous iteration but it is ordered above it by the current iteration. The best scoring move will be missed on the current iteration only if it's ordered below the stopping move.