Prophet and chess4j now understand knight outposts. An outpost, as implemented in Prophet, is a square that cannot be attacked by an enemy pawn. Putting a knight on an outpost can be a strong advantage, particularly if that knight is supported by a friendly pawn.

In the following diagram, the knight on D4 is on an outpost square, but the knight on E4 is not since it may be run off by the F7 pawn at some point.

The bonus (or penalty) given for an outpost varies by square. An additional bonus is given if the outpost is supported, such as the knight on the D4 square above. The “supported” bonus also varies by square. This is possibly overkill, but with an auto-tuner , I reasoned the more knobs and dials it has to minimize error the better. (Or at least, it can’t hurt as long as we guard against over-fitting.)

As expected this feature isn’t a huge gain in terms of ELO, but it did net a few points. It also puts the latest development version at +50 ELO over Prophet 4.2, which was my goal before doing a new release. Before doing a release I’m going to test a couple more terms, both expected to be minor gains at most, but after that I’m going to switch gears so it’d be good to clear them from the board. Those terms are “trapped bishop” and “supported rook on open file.”