🚀 go-pugleaf

In gnu.chess you write:

>Tom Vijlbrief (tom@izf.tno.nl) wrote:
>: I noticed when running some of the Bratco-Kopec tests that
>: GNUCHESS shows some strange behaviour.

>: The idea is to turn off the hashtable and let it play a move:

>----- much text deleted ------

>: =====================================
>: Note that at the first move computation ply 2 shows a tree count of 4431 .
>: After the undo the tree count at ply 2 is 4437 !!!

>: Does somebody has an explanation for this. I think that somewhere
>: a variable is uninitialised !!!

>: This is more important than it seems at first sight
>: because after the undo, gnuchess sometimes plays a much better move !!!


>The difference is due to the static cache which is not cleared following
>the undo.  If you were to add a ZeroTTable () in SelectMove () before the
>iterative deepening begins, you will find that the inconsistency will 
>disappear.  (I've tested this of course).

Too bad, I already added this myself and it makes a difference but I
got still differing node counts ! 6437 and 6337. Just trie undo-ing
the second or third move and recompute. The first move is always ok now.

Anyway, this does not explain why there is a difference in the node count.
It should only make a difference in speed, not in the node count !

It means that pruning is different when scores are taken from the
evaluation cache instead of recomputed. I can also get the difference
when I disable the cache (don't def -DCACHE)....

Any other hints ????

Tom


Your move is? go
Stage: 3
 
Move# 3    Target= 0    Clock: 0
 2.    334    0     6437   g4d1  c8c1  d1c1  d7f5 
 3&    305    0    10100   g4d1  d7f5  h2h4  c8c1  d1c1 
 3&    329    0    10766   f7g7  d7g7  c1c8  a8c8  g4c8  g7f8  c8f8  g8f8 
                           g5h7  f8g7 
 3&    364    0    12736   c1c8  d7c8  g4c8  a8c8  f7f6 
 3.    364    0    15163   c1c8  d7c8  g4c8  a8c8  f7f6 
 4-    196    1    18006   c1c8  d7c8  f7h7  c8g4  f2f3  g4f3  g2f3 
 4+    487    1    23752   f7g7  g8h8  g7h7  h8g8  h7g7 
 4&    418    2    36067   f7g7  d7g7  g4e6  g8h8  g5f7  g7f7  c1c8  a8c8 
                           e6f7 
 4.    418    4    93025   f7g7  d7g7  g4e6  g8h8  g5f7  g7f7  c1c8  a8c8 
                           e6f7 
 5&    419    5    98609   f7g7  d7g7  g4e6  g8h8  g5f7  g7f7  c1c8  a8c8 
                           e6f7 
 5.    419    7   156764   f7g7  d7g7  g4e6  g8h8  g5f7  g7f7  c1c8  a8c8 
                           e6f7 
^C 6.    419    9   192159   f7g7  d7g7  g4e6  g8h8  g5f7  g7f7  c1c8  a8c8 
                           e6f7 
8. ... f7g7
Gen 671129 Node 192159 Tree 479 Eval 8479 Rate 21351 EC 13124/7846 RS hi 0 lo 1 
Hin/Hout/Tcol/Coll/Fin/Fout = 0/0/0/0/0/0
My move is: f7g7
 
Your move is? undo
 
White 0:00  Black 0:00
 
 R - R - - - K -
 P P - Q - r - P
 - - - - - P P -
 - - - P - - n -
 - - - - - - q -
 - - - - - - - -
 p p - - - p p p
 - - r - - - k -
 
 
Your move is? go
Stage: 3
 
Move# 3    Target= 0    Clock: 0
 2.    334    0     6337   g4d1  c8c1  d1c1  d7f5 
 3&    305    0    10174   g4d1  d7f5  h2h4  c8c1  d1c1 
 3&    329    0    10840   f7g7  d7g7  c1c8  a8c8  g4c8  g7f8  c8f8  g8f8 
                           g5h7  f8g7 
 3&    364    0    12179   c1c8  d7c8  g4c8  a8c8  f7f6 
 3.    364    0    14928   c1c8  d7c8  g4c8  a8c8  f7f6 
 4-    196    1    18155   c1c8  d7c8  f7h7  c8g4  f2f3  g4f3  g2f3 
 4+    487    1    23905   f7g7  g8h8  g7h7  h8g8  h7g7 
 4&    418    2    36220   f7g7  d7g7  g4e6  g8h8  g5f7  g7f7  c1c8  a8c8 
                           e6f7 
^C 4.    364    3    66230   f7g7  d7g7  g4e6  g8h8  g5f7  g7f7  c1c8  a8c8 
                           e6f7 
9. ... f7g7
Gen 208752 Node 66230 Tree 423 Eval 3845 Rate 22076 EC 14697/8879 RS hi 0 lo 1 
Hin/Hout/Tcol/Coll/Fin/Fout = 0/0/0/0/0/0
My move is: f7g7