Author: David Hanley
Date: 17:40:44 08/29/02
Ok, i have my program working and fairly complete--it has all the rules in and plays decent positional chess. I'm pleased. I implemented all the mechanisms that i think i'm supposed to--nullmove, hash move first, then two killers, then winning static exchange moves sorted by expected material win, then moves sorted by their history score. I sort moves at the root with each iterative deepening. However, the branching factor seems 'off.' My branching factor seems to vary between 4 and 7. For example, here's an 8 ply search from the opening position: Score: -53 Searched 414821 total nodes Got 114215 hash hits (27 percent hits) There were 240894 quiesce nodes The pawn hash contains 17855 entries Branching factor is 4.522705 Here's a 6 ply search a bit later: (white just thought and chose e3) +---+---+---+---+---+---+---+---+ | R | N | | Q | K | B | | R | +---+---+---+---+---+---+---+---+ | P | P | P | | P | P | P | P | +---+---+---+---+---+---+---+---+ | | | | | | N | | | +---+---+---+---+---+---+---+---+ | | | | P | | B | | | +---+---+---+---+---+---+---+---+ | | | |*p | | | | | +---+---+---+---+---+---+---+---+ | | |*n | |*p |*n | | | +---+---+---+---+---+---+---+---+ |*p |*p |*p | | |*p |*p |*p | +---+---+---+---+---+---+---+---+ |*r | |*b |*q |*k |*b | |*r | +---+---+---+---+---+---+---+---+ Score: -44 Searched 134392 nodes Got 27504 hash hits (20 percent hits) There were 87728 quiesce nodes The pawn hash contains 6098 entries Branching factor is 5.999756 I guess i wonder if i'm fussing over nothing. Or perhaps if my search is broken somehow. I tried turning off move sorting and launched a search from the opening position. It seems to indicate to me that the move sorting is having a big positive effect. Here's a six ply search from the opening position, no move sorting: Score: -55 Searched 591677 nodes Got 128337 hash hits (21 percent hits) There were 395070 quiesce nodes The pawn hash contains 31050 entries Branching factor is 7.623291 It took more nodes than the 8 ply search with sorting! Maybe i should be happy with my code, but i hear people talking of branching factors like two and three. So maybe i should look for a bug. dave
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