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Subject: Re: Storing the PV in a search routine

Author: Guido Schimmels

Date: 04:02:57 06/12/98

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On June 10, 1998 at 13:59:09, Bruce Moreland wrote:

>...
>I made a single array, which is sized at max depth squared, plus max
>depth, all over two (   (D^2+D)/2   ).
>
>I made an another array of pointers into this array, there are max depth
>pointers.
>
>I then initialized the pointers so that the first one points at element
>0, the second one points at element D, the third points at element 2D-1,
>the fourth points at element 3D-2, etc.
>
>The point is that each of these arrays needs one less element, because
>the maximum length of the PV is shorter the deeper you already are.
>Levy calls this a triangular array, which seems reasonable to me.
>
>I was being anal about memory at the time.  If you want, you can just
>make an array that is D^2 and forget about it, it's not like we have to
>worry about blowing RAM much these days, except with hash tables.

>bruce

Exactly what I was doing for years :)
But  it has become obsolete, as I now get the PV from a special backup
table. When I get a fail high/low on those positions later in the
search,
I will not erase this information, but will store the new score along
with
it's depth and move in additional fields of this special table, so I
never
forget which positions where PV once and often have two or three
moves in the table to use for sorting.


>Another thing is that if you fail high at depth zero, you can stick the
>move you failed high on in the array, and then just terminate it at
>length 1, so you will have return a PV of sorts if you are in a
>fail-high state.

>Remember also that your array length can be undefined if you fail low.

>I actually spend some energy trying to make sure that what's in the
array is something reasonable.

>If I fail high on the move that had been the PV up until now, I don't
>kill the old PV, I let it sit in there, so I can be sure to search it
>first when I re-search.

>Also, if I fail low, I keep the old PV around, since it's the best thing
>I have.

>If I fail high on a new move, then fail low on the re-search, I put the
>PV from before the fail high back, but this is a serious decision and
>some would argue that this is wrong, and this doesn't pertain directly
>to this topic anyway.

Example from my PV table:
pv_score = 100
pv_move = e2e4
pv_depth = 5
all_score = 80
all_move = d2d4
all_depth = 6
cut_score = 90
cut_move = e2e4
cut_depth = 4

In my example the question about move sorting is, try d2d4 first,
which failed low last time, or e2e4 which was a PV move before that ?
You have experimented with those kind of stuff as I can see from the
above.
Any Suggestions ?

- Guido



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