Author: Robert Hyatt
Date: 19:45:07 02/03/01
Go up one level in this thread
On February 03, 2001 at 20:43:13, Tony Werten wrote: >On February 03, 2001 at 18:33:28, Robert Hyatt wrote: > >>On February 03, 2001 at 05:53:20, Tony Werten wrote: >> >>>On February 02, 2001 at 21:33:10, Robert Hyatt wrote: >>> >>>>On February 02, 2001 at 14:42:23, Alvaro Jose Povoa Cardoso wrote: >>>> >>>>>On February 01, 2001 at 18:37:48, Robert Hyatt wrote: >>>>> >>>>>>On February 01, 2001 at 16:27:29, Tony Werten wrote: >>>>>> >>>>>>>On February 01, 2001 at 14:19:25, Alvaro Jose Povoa Cardoso wrote: >>>>>>> >>>>>>>>Does any one tried to use just Upperbounds and Lowerbounds in hashing, ignoring >>>>>>>>ExactScore entries? >>>>>>>>My question has to do with the fact that if we use ExactScores we don´t get long >>>>>>>>PVs to feed in the next iteration, even if we extend PVs from hash. >>>>>>>>My testing shows that if we do not use ExactScore entries in the hash table, we >>>>>>>>end up with very long PVs that can be fed into the next iteration in order to >>>>>>>>aproximate the minimal tree. After all, ExactScores are rare compared to >>>>>>>>Upperbounds and Lowerbounds. >>>>>>>> >>>>>>>>Can someone comment on this? >>>>>>> >>>>>>>One of us is missing something. The PV is always exact. If you don't store >>>>>>>exact, you don't have a pv. I don't know what you get from the hashtable, but it >>>>>>>isn't a PV. >>>>>>> >>>>>>>I take my PV from hashtable and I (almost) always get a long pv, at least as >>>>>>>long as the search depth. >>>>>>> >>>>>>>Tony >>>>>>> >>>>>>>> >>>>>>>>Thank you >>>>>>>>Alvaro Cardoso >>>>>> >>>>>> >>>>>>He is talking (I think) about a PV that is cut short when you get an EXACT >>>>>>hash hit. IE in crafty, where a PV ends with <HT> which sometimes happens >>>>>>at ply=2/3/4 and results in a very short PV. I use internal iterative deepening >>>>>>to help search around this the next iteration, however.. >>>>> >>>>> >>>>>That is exactly what I was talking about. When I get an EXACT hash hit the PV is >>>>>cut short, and extending it from the hash table doesn't help much, I just get >>>>>1-3 moves from the hash, perhaps there is something wrong with my program. >>>>>Also, and in response to Dr. Robert Hyatt, I can´t execute the assignment >>>>>because my program is the portuguese version of checkers. I hope you don't mind >>>>>if I ask questions not related to the game of chess. >>>>> >>>>>Thank you >>>>>Alvaro Cardoso >>>> >>>>That is a perfectly normal problem. My PV is often shorter than it should >>>>be due to an EXACT hash hit. Nothing you can do about it, not that there >>>>is anything wrong with it. >>> >>>I still don't get how you can have a short pv if you have a exact hashhit. >>> >>>Maybe run a test where you add in your pv, the bounds it got. My guess is you're >>>last move is a BELOW_ALFA hit. ( That was a problem I had before ) >>>It was caused because I raised alfa after nullmove, sometimes making it the best >>>score and having a bogus best_move which couldn't be found in hashtable. >>> >>>cheers, >>> >>>Tony >> >>It happens all the time. You get an EXACT hash hit while searching the PV, >>so you stop and use that score instantly. How can you fill in the _rest_ of >>the PV moves since you didn't search any deeper. I see this so often that I >>eventually added the <HT> indicator to the PV to let everyone know it really >>should be longer but was cut short by an EXACT hash hit. >> >>If you never get a short PV, you have something broken somewhere.. > >But if you get a <HT> you must have searched it the previous ply, so it's still >in your tables ? Or you've searched it this ply and you should not have >overwritten it. ( or you have something broken somewhere .. ) > >Tony > >PS very strange strange that if you don't get an error you must have something >broken. No, because this is _not_ an error. It is a well-known occurrence when you hash. The <HT> can come from any of the following: 1. deep ponder search where the opponent made a different move than you expected. IE You were expecting him to play Nc3 and your PV was e5 Re1. But instead, he played Re1. After you search e5 and Nc3, you get the same position exactly and search no deeper. 2. Same as (1) but from the current search. It is possible to reach position X in more than one way, and one of those ways could have extended the tree deeper than the one you are on now, which will give you a <HT> score that is exact. 3. Something left over from an old search. 4. something from position learning if you have that. If you don't get an EXACT hit on your PV from time to time, as I said before, something is wrong. Because _anytime_ you get an EXACT hit, you don't search any deeper. How do you fill in the PV below that point? > >> >> >> >>> >>>> >>>>And you can _still_ turn in your assignment on time. Checkers is perfectly fine >>>>to test your hypothesis. :)
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