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Subject: Re: Can we use hash table at root?

Author: Robert Hyatt

Date: 06:30:05 02/01/00

Go up one level in this thread

On February 01, 2000 at 05:48:20, Tijs van Dam wrote:

>On January 31, 2000 at 21:38:39, Robert Hyatt wrote:
>>On January 31, 2000 at 16:48:41, Tim wrote:
>>>Crafty does not use(store and probe) hash table at root.
>>>How about other programs?
>>>Is there problem to use hash table at root?
>>Suppose you look up the root position before you search a single move.  What
>>do you get back?  A fail high?  etc.  There is really nothing useful to be
>>gained by probing at ply=1, and exiting without searching a single move can
>>cause some messy problems depending on how you write the code.  In my case,
>>I didn't want to exit without searching as that confuses some bookkeeping that
>>I do..
>I use hash at root for my program GKJunior. But I won't let the root search
>fail high or low on the hash, just use an exact value with its "best move" or
>use a move with not enough draft to search first. This way, a best move will
>always be found at ply=1. I have no problems and the code is not messy.

you just mentioned one messy detail.  "no fail high or low".  This means that
for _every_ hash probe, you must be checking to see if you are at ply=1 before
you do the fail high or fail low?  All for no benefit at all.

>An advantage is that the search will continue very fast when the opponent makes
>the same move as i was pondering, or to start pondering after making a move.
>There is almost no delay, while crafty seems to take a few seconds to get to the
>same PV as it had before the move was made.

I do this differently.  If I complete a 12 ply search, and start to ponder,
I ponder the 2nd move in the PV, I shift the PV two moves left to get rid of
the move I made and the move i am pondering.  I then start the search at old
depth-1 since I already have the PV from old depth-2 done...


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