Author: William Penn
Date: 17:44:17 12/09/00
(My prior post didn't display the Plus and Minus symbols correctly in the text, for unknown reasons, thus this repeat...) CM8000 position evaluations, Plus Minus Scores (repeat) The position on the chessboard can be scored as either plus or minus depending on which side has the advantage. Plus values favor white, and the larger the value the more favorable for white. Minus values favor black, and the more negative the number the more favorable for black. This is an absolute protocol to express the current status of the game, and has nothing to do with which side is on the move. Any variations from this widely understood protocol should be carefully explained, or confusion is likely to result. I have observed a related problem with CM8000 more than once. Simply, you can ask a custom personality to analyze a position for you, and it will yield certain results. Then you should be able to confirm those results by making each possible move from the position, rather than letting the software do the iteration of possible moves. That should usually give you approximately the same results at one less ply. The problem with CM8000 is that the signs of the resulting scores are apparently wrong, sometimes. Instead of plus they are minus, and vice versa. CM6000 got it right. CM8000 gets it wrong. Here's an example... Position after 1.Nf3 d5 2.d4 Nf6 3.c4 c6 4.Qc2 dxc4 5.Qxc4 Bf5 6.g3 e6 7.Bg2 Nbd7 8.Nc3 Be7 9.0-0 0-0 BR -- -- BQ -- BR BK -- BP BP -- BN BB BP BP BP -- -- BP -- BP BN -- -- -- -- -- -- -- BB -- -- -- -- WQ WP -- -- -- -- -- -- WN -- -- WN WP -- WP WP -- -- WP WP WB WP WR -- WB -- -- WR WK -- This is a well known position and white has several possible continuations, the most popular being 10.e3. Let's analyze it with Shep's CM6666 Deep and Chessmaster 6000 software, and compare that with CM8666 Deep and Chessmaster 8000 software. They give very similar results as you can see below. Variations in scores of 0.20 or less are fairly insignificant. after 9...0-0 after 9...0-0 CM6666 Deep (CM6K) CM8666 Deep (CM8K) Depth Score Moves Depth Score Moves 01/09 0.10 Re1 9 0.13 Re1 01/10 0.21 Re1 10 0.24 Re1 01/11 0.07 Re1 11 0.14 Re1 01/12 0.10 Re1 12 0.16 Re1 01/13 0.03 Re1 13 0.15 Re1 As you can see above, both programs think 10.Re1 is the best move at these ply levels. Neither finds the popular move 10.e3. Since neither program reports any information about 10.e3, the only way we can investigate 10.e3 is to make the move and see what scores result (see below): after 10.e3 after 10.e3 CM6666 Deep (CM6K) CM8666 Deep (CM8K) Depth Score Moves Depth Score Moves 01/09 -0.52 Ne4 9 0.54 Qc7 01/10 -0.41 Ne4 10 0.33 Qc7 01/10 -0.47 Rc8 10 0.42 Qa5 01/11 -0.39 Rc8 10 0.46 c5 01/12 -0.29 Rc8 10 0.50 Rc8 01/12 -0.36 Qc7 11 0.44 Rc8 01/12 -0.43 Ne4 12 0.39 Rc8 01/12 -0.46 b5 12 0.46 Ne4 01/13 -0.29 b5 13 0.42 Ne4 We see (above) that there are many possible moves with similar scores. Also we note that the CM6000 scores are all negative, but the CM8000 scores are all positive. In the series of moves at 01/10 and at 01/12 depths with CM6000, the changes are towards more negative scores. That seems proper because we are searching for the best black move. (better black positions are more negative) In contrast the trend of scores with CM8000 in the series at 10 and 12 depths is towards more positive values. That appears to be in the wrong direction when trying to find the best black move. The reason is probably that CM8000 fails to put the minus sign on the moves here after 10.e3. They should probably all be negative values, not positive values, analogous to the results with CM6000. It's OK if CM8000 wants to use a special protocol, provided it is carefully explained in the documentation available to users. Presumably that's the reason here, rather than a bug, but I don't know any easy way to distinguish between those two possibilities. Suffice to say that at this point, I'm not 100% confident about CM8000's analysis, because I can apparently never know with certainty whether a score is really plus or minus. I haven't noticed a problem (so far) when the scores are more than +1.00 or less than -1.00, but there is some apparent confusion when they are within that range. At least, I am confused!? I understand that CM8000 analyzes positions differently than CM6000. The listing of moves in the Think Lines window isn't as neatly ordered and easy to understand as CM6000. The trends don't always go in the direction expected. It may find a good move, then a blunder, then a good move, then another blunder, etc., and only the last move found has significance -- prior moves being "outdated" and their scores now incorrect. I'm told that is normal for CM8000. However I have seen the above problem with the plus/minus signs too often, so I believe there may be a genuine problem in that regard. WP
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