A tale to be told
Posted: Sun Feb 13, 2011 12:12 pm
rn1q1r2/p1p1ppkp/1p4p1/8/2BP4/2N2N2/PP3PPP/R1B1K2R b KQ - 0 11
Three minors versus a Queen is never an easy situation (the Queen usually needs targets like weak pawns, or maybe an open board for forks). IvanHoe has -36 centipawns as the material imbalance:
The overall eval() of this position is 19cp for Rybka 3, and is 25 for IvanHoe (from White's perspective in both cases).
However, a 30s search put Rybka 3 as favouring White by ~40cp, while IvanHoe calls it about equal. The reason for this, from what I can determine, seems to be in the difference in king safety evaluation in subsequent positions. For instance, after the IvanHoe PV 11...Nd7 12. O-O Nf6 13. Be3 Qd6 14. Ne5 a6 15. Rad1 b5 16. Bd3 Rac8, there are 3 White pieces attacking a square around the Black King (Be3/Bd3/Ne5). Rybka 3 values these attackers at approximately 95.4 cp (then multiplied by a 17/24 factor for the game phase, the calculation to get 954 being MemLoc0x582960[3]*530/10), while IvanHoe values them at 50 cp (as KingSafetyMult[3]*45/8, with then also a 23/32 game phase factor). This seems to me to be the principal reason behind the disparity where Rybka 3 gives an eval() of this terminal position of 79 cp, while IvanHoe only 15 cp. In general, I could comment that IvanHoe appears to put greater relative weight on majors attacking the opponent King (see Appendix A.2.2 of the R3/IPPOLIT report for brief data).
Three minors versus a Queen is never an easy situation (the Queen usually needs targets like weak pawns, or maybe an open board for forks). IvanHoe has -36 centipawns as the material imbalance:
Material [index 360718]: RRBBNNPPPPPPqrrnppppppp -> BBNqp values: 10:-32:-101:-140 phase 23 -> -36
The overall eval() of this position is 19cp for Rybka 3, and is 25 for IvanHoe (from White's perspective in both cases).
However, a 30s search put Rybka 3 as favouring White by ~40cp, while IvanHoe calls it about equal. The reason for this, from what I can determine, seems to be in the difference in king safety evaluation in subsequent positions. For instance, after the IvanHoe PV 11...Nd7 12. O-O Nf6 13. Be3 Qd6 14. Ne5 a6 15. Rad1 b5 16. Bd3 Rac8, there are 3 White pieces attacking a square around the Black King (Be3/Bd3/Ne5). Rybka 3 values these attackers at approximately 95.4 cp (then multiplied by a 17/24 factor for the game phase, the calculation to get 954 being MemLoc0x582960[3]*530/10), while IvanHoe values them at 50 cp (as KingSafetyMult[3]*45/8, with then also a 23/32 game phase factor). This seems to me to be the principal reason behind the disparity where Rybka 3 gives an eval() of this terminal position of 79 cp, while IvanHoe only 15 cp. In general, I could comment that IvanHoe appears to put greater relative weight on majors attacking the opponent King (see Appendix A.2.2 of the R3/IPPOLIT report for brief data).