Author: Don Dailey
Date: 08:47:13 12/02/97
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On December 01, 1997 at 11:25:35, Marcel van Kervinck wrote: >On November 30, 1997 at 06:41:25, Don Dailey wrote: > > >Don wrote: > >>My position is that bit boards are "probably" better in the long run but >>I will be willing to change my mind if it turns out I am wrong. I also >>argue that dynamic knowledge is more easily and more efficiently >>implemented >>with bit boards. I don't mind taking a commital position here because >>I >>can always change my mind later! I would like to see this discussion >>continue because there may be much to be learned. > >Could you elaborate a bit on the use of bitboards in CilkChess? >Eg, how much did you gain in raw speed by converting to them on the >alphas, and how does it compare to Crafty on the same hardware? > >The reason I ask is the silly test we did just after the last >round in the Dutch open, yesterday. If I recall correctly, my >non-bitmap program searched about 120 knps on your machine in >the starting position. Based on the Sparc results, I would expect >it to the reach 150+ in a typical middlegame position without any >effort. I don't think it can run much faster than that, however. >You said your program computed at about the same speed, but that >there is quite some new knowledge overhead. Can it grow there? > >Marcel van Kervinck Hi Marcel, It sounds like we are computing about the same number of nodes per second, but I'm using bitboards. I personally do not believe bitboards are a big win if you just want a really fast program but perhaps Bob or others will disagree (or agree.) Since I am new to bitboards it could also be that case that I'm doing a few things wrong. A lot of people have been pressuring me to add a lot more knowledge to my program. I did an autotest study which indicated a knowledgable program will improve more with depth (which was the opposite of my intuition.) So with the new Cilkchess using bitboards, I decided to not be overly concerned about the overhead of lots of knowledge. This program has more knowledge than my others (depending on how you count heavily pre- processed stuff) I think it has been typical for my programs to spend no more than a few percent of time on evaluation (maybe 15-20% ??) but this one spends more than half its time. I think this was improved by some of the local whiz kids here at MIT but it's still quite expensive. I'm pretty convinced bit boards are the way to go for a knowledge intensive program but there is an ongoing debate about this and some would not agree. I can state with confidence that this program would not have the same QUANTITY of knowledge and still be reasonably fast if it were not using bitboards. It is really difficult to define how much knowledge a program has. When people talk about how many TERMS in their evaluation function or speak of knowledge like it's a quantity (like I just did!) it can get confusing. A really good pre-proccessor can package up a lot of chess concepts into a really tight package and there seems to be no reasonable way of measuring this. You cannot say, "my program has a IQ of 50 chess principles" and it mean much. But I am saying that I think I've captured a lot of chess concepts that my other programs ignored and it has proven to be somewhat expensive. A lot of it could be approximated cheaply with piece/square pre-proccessing. I'm going to persue this however, look for cheaper ways to say the same things and we are now working specifically on recognizing compensation for a pawn or exchange. I hope the program does not slow down too much. I would like to see you experiment with bit boards if you feel inclined. I think we need a lot of people doing this to answer the question of which approach is better if any. If you decide to do this keep in touch please. I'm interested in other experiences with them. I want to hear from people especially who have done both. Does your evaluation comsume a lot of time? If not, your program should run much faster with bit boards than it did last Sunday on our Alpha. It's hard to say however without either of us knowing too much about the details of both programs. Like Crafty, we don't have any secrets here and I'm willing to share the ideas and implementation details of our stuff. Our program is still extremely new so I don't know how things will look in the future. I think we are capable of much better than what we saw in this tournament. Even though 9 1/2 and clear second seems like a good tournament, we had 4, 466 mgz Alpha's versus only Pentiums. Most programs would have done quite well too with our hardware. Don
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