Sorry for the misunderstanding on my part. I thought you were one of those who think Stockfish is a clone of Rybka. :)

Stockfish scores the position as +2.x.

If you want to know the back story, the open-source Glaurung engine developed by Tord was kind of "put on hold" when Tord went to pursue other interests. Marco came along and made various improvements to Glaurung and named it Stockfish, also released under GPL. In that sense it isn't really a "clone," which is a word with negative connotations, but rather a "fork," or divulgence from the path.

Decreases the scores for such positions (and therefore tries to avoid them when ahead and seek them when behind).

Vas

I just meant that the score would have been even higher without the heuristic.

Vas

> I agree. BU irrelevant.

I once played a game which needed BU to avoid stalemate (Queen or Rook we stalemating) and it was delivering a quick mate. I was very excited to see that. My opponent resigned immediately when he saw me under promote to a bishop :)

All this talk about BU being irrelevant is nonsense. Just have a separate version for it,
or a UCI switch, and be done with it!

Andrew

I think this is a very complicated issue, and to be honest I would leave it at default for play and maybe play with it for analysis.  It is no secret that Rybka 4 will go into a drawn rook endgame a pawn up with a very high evaluation.  In most cases no damage is done as the game would have been drawn anyway, but in some cases (which I have tested) R4 will give up a huge winning advantage and simplify into this drawn rook endgame and end up losing half a point.  In those games during analysis, I did play around with rook endgame scaling and managed to avoid the simplification of rooks and it ended up winning the game.  I think I used a rook scaling of average 60 to avoid the simplification.  I would definitely not use it in game play as it probably does more harm than good.

The more I have seen R4 games the more I have toned down my criticism of its endgame play, and I think I now understand why Vas has left it as it is.  R4 wins some pretty amazing games by simply outplaying its opponent in rook endgames.  The overly high evaluation makes R4 be quite aggressive and dynamic, and in many cases it will squeeze out a win.   It is most likely the best compromise for R4 at the moment.  Of course it is hugely frustrating when R4 avoids a winning endgame to simplify into an obvious rook endgame, but if you look at an endgame book you will see that 3/4 of it is only about rook endgames.  That is not unusual since 10% to 15% of games end up in rook endgames, so it is significant.  I am not sure how much 3/4 of a book of heuristics is in chess code, but most likely it is a major project.

By the way, rook endgame play by R4 can be greatly enhanced by having the relevant 6 man EGTB's.  I am sure you can find info on that if you do a search.  Am not sure how many GB the relevant rook EGTB's are, but they should be reasonably manageable.