..............

43...Qg8 44.Re1 b3 45.Qxc3

µ (-0.96) Depth: 18 00:30:42 420851kN, tb=39

43...Qg8

µ (-1.16) Depth: 19 00:41:14 580575kN, tb=44

43...Qf7 44.Re1 b3 45.Qxc3

µ (-1.19) Depth: 19 01:19:32 1154675kN, tb=134

43...Qf7 44.Re1 b3 45.Qxc3 Rxa4

µ (-1.19) Depth: 20 01:49:52 1610549kN, tb=149

43...Qf7

µ (-1.39) Depth: 21 04:49:13 160019kN*, tb=1513

43...Qg8** 44.Re1 b3 45.Qxc3

µ (-1.22) Depth: 21 05:01:31 294324kN, tb=10837***

and is now showing (after 8 hours) that she is thinking of 43...Qg8 (1/30) at depth 22.

Notes:

* don't mind this, my system is known to reset the total node count after a 2-3 hours; it was the same with R232a

** so she chooses a move with lower evaluation (-1.22 over -1.39)???

*** this is also weird, watch the rate tbs are accessed, it is almost impossible that she accessed so many of them (from 1513 to 10837) in only 12 minutes or so (from 4h49m13s to 5h01m31s)??!

The number of tablebases accesses is perfectly normal. If I use Deep Shredder and tablebases are on a SSD, I get up to 10000 TBAs per second.

As for tablebases, there is a nonproportional access rate between reported 4h49m13s and 5h1m31s, which is about 9000 tb positions for only 12 minutes, compared to previously reported rates. I expect this to slightly increase (access rate that is) as search gets deeper, but this is too huge a jump. This itself is not wierd, it is unexpected when you check access rates previously! This is a 22-men positon on board, and there is no logic for sudden speed up in tb accessing.

> WHY would engine choose move with lower evaluation???

Unless your GUI reports scores for the side-to-move, this is a bug. :)

> As for tablebases, there is a nonproportional access rate between reported 4h49m13s and 5h1m31s, which is about 9000 tb positions for only 12 minutes, compared to previously reported rates.

Qg8 might lead to TB positions at just the right moment (i.e. the lowest depth at which TBs are accessed).

My GUI reports + for white, and - for black. It's standard, though old, CB8 that came with Shredder9. So obviously, something is wrong here.

"Qg8 might lead to TB positions at just the right moment (i.e. the lowest depth at which TBs are accessed)."

It might, but look at previous depths, where Qg8 emerged on top, only a few tb access. Can't change all that dramaticaly for this move in a matter of 1 or 2 plies?!

> Can't change all that dramaticaly for this move in a matter of 1 or 2 plies?!

Of course it can. If the positions are now reached at the cut-off depth, the depths would've been below the cut-off depth in previous iterations (=no TB accesses).

Here's the depths, times and Tbs:

d14 00:02:07 tb=1

d15 00:02:07 tb=1

d15 00:02:07 tb=1

d15 00:02:55 tb=2

d16 00:03:34 tb=2

d17 00:12:40 tb=7

d18 00:30:42 tb=39

d19 00:41:14 tb=44

d19 01:19:32 tb=134

d20 01:49:52 tb=149

d21 04:49:13 tb=1513

d21 05:01:31 tb=10837

> how come she accessed it first time at depth 14 and after only 2 minutes search?

Before then, all lines that reached the TBs did so at depths lower than the cut-off depth.

*>Then, as she goes through the rest of the moves (still at depth 21!), she chooses 43...Dg8*

No - she doesn't go through the rest of the moves, but finds something that makes her see that Qf7 isn't that good as she thought.

To verify that you might make an anylysis of Qf7 later.

after finishing depth 20, Rybka displays following as the best line/move:

43...Qf7 44.Re1 b3 45.Qxc3 Rxa4

µ (-1.19) Depth: 20 01:49:52 1610549kN, tb=149

Now, she moves to depth 21. Obviously, the first considered move is 43...Qf7 (1/30). She takes some time, and after a couple of hours, she displays following:

43...Qf7

µ (-1.39) Depth: 21 04:49:13 160019kN, tb=1513

which is supposed to mean that she found that her best move so far is even better by 20 cp points.

Now she moves on with the rest of the candidate moves (to see if there's even better move), and after only 12 minutes is able to tell

a) oh wait, there's a problem with 43...Qf7 (even though she was considering only 43...Qg8 at this point, and just spent 2-3 hours on 43...Qf7)!

b) doesn't display what is the problem (she might have displayed something like 43...Qf7 with say -0.98 evaluation, but this is irrational, usually when things go up (fail highs), things go up even more later at the same ply)

c) changes to 43...Qg8.

... and now as I see she refuses to display anything at depth 22, althoug she moved now to 43... Qf7 (2/30) at depth 22.

> No - she doesn't go through the rest of the moves, but finds something that makes her see that Qf7 isn't that good as she thought.

That's not how it works. I'm pretty sure Vas would report another Qf7 PV with a lower score (probably as upperbound) if this was intentional behaviour.

>Don't you see? R3 finishes depth 20 with 43...Qf7 as best move for black, with 1.19 evaluation for the black side. Then, at depth 21, she sees that >the same 43...Qf7 is worth even more, 1.39. Then, as she goes through the rest of the moves (still at depth 21!), she chooses 43...Dg8, although >this move brings "only" 1.22. WHY would engine choose move with lower evaluation???

D20 Finishes the search and says Qf7 is the best move with -1.19 score.

D21 Starts thinking about Qf7 and thinks it is -1.39. Prints it on the screen. Continues thinking on it(while you don't see it since it doesn't report it--it doesn't print it) and finds that Qf7 is actually worth less than -1.22. Starts thinking on Qg8 and finds it to be -1.22 so it prints the result in the screen as the best move.

In the current GUIs, because it may be related to the new Chessbase GUI that will come with Rybka 3. It may have another behavior in the new Chessbase Rybka 3 GUI as i've seen a new pane that will report Rybka's evaluation in some other way.

Look at this position:

Analysis by Rybka 3 1-cpu 32-bit :

22...Bf5-e6 23.Qg2-f2 Kg8-h8 24.Ra1-d1 Rd3xd1 25.Rf1xd1 Nc6-d4 26.Nd5-e3 Ra8-d8 27.b2-b3 b7-b6

-+ (-1.66) Depth: 8 00:00:01 15kN

22...Bf5-e6 23.Qg2-f2 Kg8-h8 24.Ra1-d1 Rd3xd1 25.Rf1xd1 Nc6-d4 26.Nd5-e3 Ra8-d8 27.b2-b3 b7-b6

-+ (-1.66) Depth: 9 00:00:01 30kN

22...Bf5-e6 23.Qg2-f2 Kg8-h8 24.Ra1-d1 Rd3xd1 25.Rf1xd1 Nc6-d4 26.Nd5-e3 Ra8-d8 27.b2-b3 b7-b6 28.Rd1-f1

-+ (-1.61) Depth: 10 00:00:02 49kN

22...Bf5-e6 23.Qg2-f2 Kg8-h8 24.Ra1-d1 Rd3xd1 25.Rf1xd1 Nc6-d4 26.Nd5-e3 Ra8-d8 27.b2-b3 b7-b6 28.Rd1-f1

-+ (-1.61) Depth: 11 00:00:03 70kN

22...g6-g5 23.Bh6xg5 Bf5-e6 24.Qg2-e4 Rd3xd5 25.c4xd5 Be6xd5 26.Qe4-e3 Nc6-d4 27.Bg5-h4 h7-h6 28.Rf1-f2 e5-e4 29.Bh4-g3 e7-e5 30.Ra1-d1

=/+ (-0.39) Depth: 12 00:00:59 1564kN

22...Nc6-d4 23.g4xf5 Rd3-g3 24.Qg2xg3 Nd4-e2+ 25.Kg1-g2 Ne2xg3 26.Kg2xg3 g6xf5 27.Bh6-g5 f5-f4+ 28.Kg3-h4 Kg8-f7 29.Rf1-d1

=/+ (-0.67) Depth: 12 00:01:31 2622kN

22...g6-g5 23.Bh6xg5

=/+ (-0.39) Depth: 13 00:02:42 4695kN

22...g6-g5 23.Bh6xg5 Bf5-g6 24.Ra1-d1 Rd3-d4 25.Qg2-f2 b7-b5 26.b2-b3 Ra8-b8 27.Qf2-h4 Rb8-e8 28.Qh4-f2

=/+ (-0.29) Depth: 14 00:03:20 5875kN

You will notice that Rybka avoids giving too much information about fail low and fail high.

At depth 11 it gives Be6 as -1.61 while at depth 12 and without any apparent reason(to show that Be6 is bad) it gives g5 as better with -0.39.

Obviously Rybka found at depth 12 that Be6 is bad and "below" -0.39(actually above -0.39 since we are speaking about negative numbers), but didn't report it, it didn't print it on the screen.

>What's the Problem? Rybka found out at depth 21 that Qf7 isn't as good as she first thought - so she switched to Qg8.

Exactly, Rybka 3 found that Qf7 move on ply 21 has an evaluation of less than -1.22 so it preferred Qg8 that has -1.22.

Perhaps Qf7 had a score of exactly -1.22 and according to Vas for older Rybka's(i don't know if this still exists) Rybka 3 have chosen at random the move between Qf7 and Qg8 that had the same score.

As for tbs accesses i don't see any problem. Obviously tbs accesses have also been reset so that 1513 at ply 21 was actually much more. So the 10837 is normal.....

This crossed my mind, but still the discrepancy is huge, and I've never seen TB count reset so far, while I see total node count reset EACH time (somewhere between 2h30m and 3h).

43...Qg8 44.Re1 b3 45.Qxc3

µ (-1.22) Depth: 21 05:01:31 294324kN, tb=10837

Now this behaviour I've seen sometimes, at Naum I think, and maybe Zappa (or was it Crafty?).

> WTF??

The earlier PV failed low, she tried to find another move (it'd have saved a lot of time) but couldn't, and returned to searching the PV move with a widened window.

I can't think of any other reason this would happen.

Anyway, thanks Vempele, Kullberg and George for putting up with me on this one. :-)

And Arkansaw, of course. :-)

Edit: now I expect Vas to come and say "We'll add this to FAQ." :-)

µ (-1.19) Depth: 20 01:49:52 1610549kN, tb=149

43...Qf7

µ (-1.39) Depth: 21 04:49:13 160019kN*, tb=1513

43...Qg8** 44.Re1 b3 45.Qxc3

µ (-1.22) Depth: 21 05:01:31 294324kN, tb=10837***

What apparently happened here is that 43. .. Qf7 first failed high at depth = 21 (Rybka's window is 20 centipawns) and then during the research failed low (which is not reported). This is rare but can happen.

Vas

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