Quiescence search

It mitigates the effect of the horizon problem faced by AI engines for various games like chess and Go.

As the main motive of quiescence search is to get a stable value out of a static evaluation function, it may also make sense to detect wide fluctuations in values returned by a simple heuristic evaluator over several ply, i.e. a history criterion.

In highly "unstable" games like Go and reversi, a rather large proportion of computer time may be spent on quiescence searching.

The horizon effect is a problem in artificial intelligence which can occur when all moves from a given node in a game tree are searched to a fixed depth.

This can result in the peculiar ploy of a program making delaying moves that degrade the position until it pushes a threat beyond the search depth or "horizon".