====== Chess - Programming - Horizon Effect ======

The **Horizon Effect**, also known as the horizon problem, is caused by the depth limitation of the search algorithm.

  * Because only a partial game tree has been analyzed, it will appear to the system that an event can be avoided when in fact this is not the case.
  * Besides obligatory Quiescence search, Extensions, especially Check Extensions are designed to reduce horizon effects.

When evaluating a large game tree using techniques such as Minimax with Alpha-Beta pruning, search depth is limited for feasibility reasons.

  * However, evaluating a partial tree may give a misleading result.
  * When a significant change exists just over the horizon of the search depth, the computational device falls victim to the horizon effect.

----

Greedy algorithms tend to suffer from the horizon effect.

The horizon effect can be mitigated by extending the search algorithm with a quiescence search.

  * This gives the search algorithm ability to look beyond its horizon for a certain class of moves of major importance to the game state, such as captures in chess.

Rewriting the evaluation function for leaf nodes and/or analyzing more nodes will solve many horizon effect problems. 

----

[[Chess:Programming:Horizon Effect|Horizon Effect]]