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Subject: Extensions?!

Author: Dan Homan

Date: 06:08:49 01/13/98

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On January 12, 1998 at 14:49:17, Robert Hyatt wrote:

>On January 12, 1998 at 14:23:02, Dan Homan wrote:
>
>>Test Position: WAC 003
>>
>>  +---+---+---+---+---+---+---+---+
>>8 |   |   |   |   |   | *R| *K|   |    White to move
>>  +---+---+---+---+---+---+---+---+
>>7 |   | *P| *P| *B|   |   |   | *P|    castle: -
>>  +---+---+---+---+---+---+---+---+
>>6 | *P|   | *P| *B|   |   |   |   |
>>  +---+---+---+---+---+---+---+---+
>>5 |   |   |   |   |   |   | *Q|   |
>>  +---+---+---+---+---+---+---+---+
>>4 |   |   |   | P |   | *P|   | *R|    fifty: 0
>>  +---+---+---+---+---+---+---+---+
>>3 |   |   | P |   | R |   |   | P |
>>  +---+---+---+---+---+---+---+---+
>>2 | P | P |   | B | Q |   | P |   |
>>  +---+---+---+---+---+---+---+---+
>>1 |   |   |   |   |   | R | K | N |
>>  +---+---+---+---+---+---+---+---+
>>    a   b   c   d   e   f   g   h
>>
>>
>>White to Move  Book Move: Rg3;
>>
>>Press 's' to search, 'n' for the next position, 'q' to exit: s
>>Please enter a search time (in seconds): 30
>>  3.    154     0     1300   e3g3 g5g3 h1g3
>>  4.    313     0     5297   e3g3 d7g4 g3g4
>>  5.    313     0    10408   e3g3 d7g4 g3g4
>>  6.    313     2    53982   e3g3 d7g4 g3g4
>>  7.    313     5   174534   e3g3 d7g4 g3g4
>>  8.    313    20   735301   e3g3 d7g4 g3g4 h4g4 e2e6 g8h8
>>                              h3g4 g5f6 f1e1 f4f3
>>
>>node_count = 885911 quiescent nodes = 82048 eval_count = 183571
>>hash hits = 74864 hash moves = 9095 pawn hash hits = 173696
>>node_rate = 36912 null cutoffs = 167276 extensions = 15099
>>
>
>I tried this to a depth of 8 plies (which I assume the above means
>you reached?)  Total time was 2 seconds, with a hash hit rate of 99%.
>I re-ran it to 30 seconds and was able to search 11 plies deep this
>time, and the pawn hash hit rate was still 99%.  I used 5mb for the
>pawn hash, where one entry is 20 bytes.
>

I was just looking at these numbers and noticed that you are reaching
depth 8 in just 2 seconds!  It takes me 20 to reach depth 8 (time to
complete the first PV on depth 8, the rest of the moves at depth 8
take still more time).  This is a factor of 10!  Even assmuning a
generous factor of 3 in nps advantage, crafty is searching about a
factor of 3 fewer nodes!

I can think of a few reasons that my search would have more nodes, but
none of them should be a factor of 3.  One thing that did occur to me
is extensions.  I turned off all extensions and researched this
position.  In doing so, I found that I searched only about 30% of the
nodes to reach the same depth as the above example.  Should my
extensions really be tripling the size of my search tree?

I like the extensions a lot, just adding them in has increased my
program's blitz rating on FICS by 200 points (now about 2030).  I am
wondering, however, if I have overdone it.  What do you typically
expect the increase in tree size to be with reasonable extensions?

 - Dan

p.s. My program does

capture extensions    (4/10 of a ply)
re-capture extensions (1 ply)
check extensions      (1 ply)
pawn push extensions  (1/2 ply or 1/3 ply)  (endgame and late
middle-game)
bruce's mate ext.     (1 ply)



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