From: Jeroen Tiggelman <Tiggelman <at> CONSUL <dot> NL>
Date: 11 dec 1996
Subject: Re: Evaluation (was Re: Computer Shogi)

Michael Facer <michaelf @ LAVA.NET> wrote:
>Why is a promoted pawn worth less than a gold? [...]

I replied to this part in another mail.

>A promoted Bishop is supposed to be worth 3 silvers?
>Is there anybody out there who wouldn't jump at the
>chance to take the three silvers? Usually I'd be happy
>to trade the promoted bishop for two silvers (assuming
>they are the king's guards).

I think the clue is that a _defending_ Horse is considered
to be worth three generals, and let me tell you that I think
that this is right. An _attacking_ one is worth considerably
less, so I'd trade it for two defending Silvers as well in
most cases. ;-)

I think the clue is that when you're exchanging the attacking
Horse for the Silvers, you're on the attack, and you don't
care as much what your opponent gets anyway, too.. ;-)
This also covers your other observations in this paragraph,
I think.

>Mr.Aono also says that good shape is the basis of good
>shogi.  At the start of a game, one can perhaps talk about
>the relative value of the pieces, but after that, the immediate
>goal is to create good shape for oneself, and if possible bad
>shape for one's opponent.

This is true, but it might be so that the evaluation would have
modifiers for the phase of the game... it is obviously not true
that the piece's value suddenly becomes _entirely_
unimportant..

>The value of good shape is worth more than material.

I think that good shape ensures that you won't easily lose
material in the future. Perhaps one should add some sort
of border conditions on minimal defense required, pieces
in hand, etc.

>One of the fundamental techniques of shogi is to sacrifice
>material in order to give your opponent bad shape.

Yes, but the material you are talking about mostly consists
of pawns, unless you also can see how to use the bad
shape... else it is usually just a bit premature...

But you may count the number of moves required to reinstall
the structure as good shape, and give a value to that...

Bad shape == point for attack

>The value of any one piece is directly related to its position
>and to the relative position of every other piece in the game.

I think that that is a slight overstatement.. But keep in mind that
the fact that your opponent doesn't have much in hand _now_
should not be taken as an encouragement for allowing gaping
holes in your camp..

>The value of any piece can change with every move.

That isn't useful for an evaluation function, though...

>In Shogi, the essence of good strategy is to attempt to refute
>material value tables such as you have listed.

That is not only in Shogi. Since each player starts with the same
material, the entire idea is to use it more effectively. It's a matter
of how close you stay to immediate moves, I think. ;-)

>By the way, I think the reason that material is so much more
>important in chess is because it can be used up.

Yes, in the sense that in Shogi you cannot really simplify the
position, so you have to go in for a complex fight. It is also
the paratroopers in another way: you cannot predict where
the opponent is going to strike, and you cannot just hold
the frontier, as in chess you can: often the fight is about a
few (center) fields, with each adding pressure to those...
But in shogi the pieces are realteively to weak to even be
able to all participate in such an attempt..

Jeroen