Author: Robert Hyatt
Date: 07:33:22 01/31/02
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On January 31, 2002 at 03:35:50, Ed Schröder wrote: > > >Is this really you Bob? > >I have seen Cray Blitz playing, Mike Valvo in ecstasy calling through the >microphone to the participants and spectators, "Cray Blitz is hitting the 9th >ply folks!". And all the programmers trembled all over, myself included, gee 9 >plies, who can win from that hardware monster. > >We are talking about Munich 1986, Cray Blitz was considered somewhat faster than >Hi-Tech from Hans Berliner. Hi-Tech searched 8 plies average in the middle game >and so did Cray Blitz. Been there, seen it. Not in Cologne it didn't. I still have the logs. Cray Blitz searched to 9 plies on occasion and 10 plies many times. I can certainly post one if you want to see it. We were searching 8 plies in 1983 at 40K nodes per second on a dual cpu XMP... > >Hi-Tech was able to get a 100K NPS, you somewhat higher, period! We were doing 200K-300K as I said. If you are talking about the Summer when the WCCC was held, we were doing 200K. If you talk about the Fall, Cray had a faster machine and we were doing 300K. I was talking about the latter... > >With a 100K NPS you typically search 8 plies (brute force!) in the middle game >and not 10-12 plies as you imply. I'm not going to make this a big argument as I wrote the thing and in COlogne you could _not_ see Cray Blitz's output. Because I was operating Cray Blitz in Birmingham and relaying just the best move to Harry... I have no idea what you thought you saw, but it wasn't _my_ program. As I said, in 1983 we were doing 8 plies, _just_ like Belle which was running at 160K nodes per second with a somewhat less efficient hardware search. In 1986 we were hitting 9 all the time and saw 10 about every third search or so. Deep Thought in 1989 was a ply or two deeper than us... and in 1989 we were doing 10 all the time at about 500K nodes per second... > >Say 200K is good for 8 plies average, being 1000 x faster with a branching >factor of 4 gives: 4x4x4x4x4 = 1024 -> 5 extra plies. > >So with 200M NPS you might be able to search 13 plies brute force in best case. > >Subtract a couple of plies (1 to 3) for the way DB did singular extensions and >the picture fits, that is: DB was searching 10-12 plies as the log files >confirm. > >This 12(6) isn't 18, you must have misunderstood its meaning. > >Ed Did you see the email from the DB team? Is there any misunderstanding that? It seems pretty clear to me. And although I busted the math yesterday, here is a better analysis: their branching factor was roughly 4, obtained from their logs. that means that they multiply the time by 4 for each iteration. Looking at their logs, they typically searched to 10(6) or 11(6). On occasion they got to 12(6) but it seemed to timeout before finishing so I didn't count those. 10(6) is 16 plies according to Hsu. I tried Crafty on several opening, middlegame and endgame positions. I averaged the total nodes searched for a 1 ply search and got roughly 100. 16 plies requires 4^15 more nodes than 1 ply... 4^15 is 2^30, which is one billion. They need to search 100 billion nodes to get to depth=16, if we assume their q-search looks something like mine. 100 billion nodes only needs 1000 seconds if they searched 100M nodes per second. But we know they averaged 200M according to Hsu/Campbell, which drops that to 500 seconds. And we also know that deeper searches might not always need that many nodes to complete when move ordering is good and hashing is lucky. I don't see _anything_ that says they can't reach 16-17 plies on normal searches, and go beyond that in special cases. Crafty seems to search about 12 plies or so in the 60 10 time controls we used in CCT, but on occasion it will run out to 15 or 16 in certain types of tactically obvious positions...
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