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Why doesn't Fritz "know" this?



 
 
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  #1  
Old July 29th 03, 10:43 AM
Neil Coward
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Default Why doesn't Fritz "know" this?

I'm no expert on this matter like Mhoulsby and Russell Reagan seem to be but
I just think a computer has to calculate everything whereas in some
positions, for humans, it is 'obvious'.

For example a 16 move mate in some positions might be easier for a human to
calculate, indeed the computer might not calculate that far, it may only be
programmed to go 8 or 10 moves ahead.

So how can a human calculate a 16 move mate better than a computer?
Imagine this position, white king on e1, black king on e8, white pawns on a2
and h2.

Now we know that black can't stop both the pawns, he goes after one, the
other queens then king and queen mate the king. This is dead easy for us
humans, but a computer, unless it has this position programmed into it, has
to work it all out.

The example you quoted, where black ends up with a rooks pawn and wrong
coloured bishop to queen, well it seems to me unless this knowledge was
programmed into the machine - just a simple bit of logic to say bishop has
to be same colour as queening square of rooks pawn - then the computer has
to sit and work it out and the drawn ending you speak of may be 20 moves
down the line, the computer hasn't calculated that far.



"Dan Scoones" wrote in message
...
Hi all,

The other day I was analysing the game Popovic-Bagirov, Moscow 1989
(Chess Informant, Volume 47, game 159.) When I reached the position
White: Kg1 Bf5 Ph2,g5,e5 Black: Kf8, Ph7,g7,f6,b6, I switched on
Fritz 8.

Black, on move, is a piece down and struggling to draw.

After 1...fxg5 2.Bxh7 Kf7 3.Bf5! (safeguarding the e-pawn) Black
resigned.

If 1...g6 2.Bxg6! hxg6 3.gxf6, and White wins the pawn ending.

The main point of interest is what happens after 1...h6. In his
annotations Popovic gives 2.gxh6 (a little joke; 2.gxf6 comes to the
same thing) 2...gxh6 (or 2...fxe5 3.h7! and wins) 3.e6! With this
move White preserves the vital e-pawn and wins easily.

If instead 3.exf6? then Black draws with 3...Kf7! followed by
4...Kxf6. The point is that a rook pawn and a bishop cannot win
against a lone king if the bishop does not control the queening
square. This, of course, assumes that Black's king can safely arrive
there himself to set up a blockade. This is a fundamental piece of
endgame knowledge possessed by all serious players.

The question is, why doesn't Fritz "know" this? In the position after
2...gxh6 in the last variation above it insists on showing 3.exf6? as
a winning line. Should the program really have to analyse for many
moves and finally reinvent the wheel before changing its "mind" and
playing the correct move? How difficult is it to build in this sort
of endgame knowledge?

Cheers,
Dan



  #2  
Old July 29th 03, 02:12 PM
henri Arsenault
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Default Why doesn't Fritz "know" this?

There does seem to be an occasional evaluation bug in Fritz8- at least
in the infinite analysis mode.

A number of times, Fritz has given an obviously bad move a (= 0.00)
rating, independently of how long I wait. But if I play the move, it
immediately shows it to be worth as low as -6. This is always
characterized by the display not showing any moves for this particular
move - just the first move. Clearly it is not kept as part of the
analysis. This has always happens as much as I can remember when the
position being analyzed was losing.

Unfortunately I did not save the positions, but it has happened more
than once or twice. It is not so serious in analysis, since it is so
obvious, but if Fritz does this while playing, then it could affect its
performance (unless it only happens when already losing).

Henri
  #3  
Old July 29th 03, 05:28 PM
Russell Reagan
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Default Why doesn't Fritz "know" this?

"henri Arsenault" wrote

There does seem to be an occasional evaluation bug in Fritz8- at least
in the infinite analysis mode.

A number of times, Fritz has given an obviously bad move a (= 0.00)
rating, independently of how long I wait. But if I play the move, it
immediately shows it to be worth as low as -6. This is always
characterized by the display not showing any moves for this particular
move - just the first move. Clearly it is not kept as part of the
analysis. This has always happens as much as I can remember when the
position being analyzed was losing.

Unfortunately I did not save the positions, but it has happened more
than once or twice. It is not so serious in analysis, since it is so
obvious, but if Fritz does this while playing, then it could affect its
performance (unless it only happens when already losing).


This might be a situation where a computer uses kind of lazy repetition
detection. Many programs do this. Basically they don't check for 3-fold
repetition. Instead, they only check for 2-fold repetition, and if a
position occurs twice, the computer assumes that it will occur a third time.
The computer works in a way such that it assumes both players are playing
perfectly (it's not really true, but that is how the computer "thinks" about
its move). To learn more about why this might have occured, read Bruce
Moreland's webpage:
http://www.brucemo.com/compchess/pro...repetition.htm


 




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