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Subject: Re: triangular pv vs. hash move pv

Author: Michael Henderson

Date: 21:39:57 09/10/04

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On September 11, 2004 at 00:08:20, Stuart Cracraft wrote:


>Which should I trust? Seems like the hash table is getting
>overwritten with other variations (not sure why). What
>kind of scenario would cause that? My algorithm is
>length >= depth to replace.

You should always trust the triangular array...since nothing funny is happening
there.  Hash table moves may vary based on depth for the entry.

>Seems like triangular would be better and then use that to
>prefill the hash table from the last iteration before the
>next iteration would be best, as Bob Hyatt mentioned.

it works well :)

>In looking at both pv's, they look fine and lead to positions
>that are often equal in material without any gross material errors that
>could be attributed to a misimplementation but there are definite
>differences between the two methods for me.

You have it working correctly

>Before I throw out the walk-the-hashtablepv, I want to be sure
>that it is really no good. So I want to know exactly how a hash
>table can be damaged such that its PV is corrupted. Under precisely
>what circumstances can this happen?

Hyatt mentioned extensions having something to do with this...i forgot what is
was though.  What I figured out is that since the hash table does not store path
info, you might start getting stupid moves because the entry is not true to the
position in the PV.


>I would have thought length >= depth would have prevented it as long
>as there are no collisions. My hashkey is 64-bits and I am searching
><1M nodes per move for my 1 second searches so I'd expect no collisons.
>Should I have some hook in there to check the collisions aren't happening
>and are causing damage to the pv or is there another hash table side
>effect that results in that damage?

I don't think you should worry about this since it's very rare :)

Michael

>
>Thanks all,
>
>Stuart



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