promotion: value of promote-to?

[hgm]

http://www.talkchess.com/forum/viewtopi ... 04&start=0

[Andres Valverde]

8/5k2/4p3/4Pp1p/5P1P/3Rn2K/6p1/8 b - - 0 1

PET #26

[Sven]

http://www.talkchess.com/forum/viewtopi ... 04&start=0

Thanks for the link to this thread which contains a couple of examples (also thanks to Andres!). In principle my logic seems to be correct, except for this part:

The only case I can imagine where the additional bishop is not redundant is that "W" has only a knight, so two knights would draw but bishop+knight win. But I failed to build a case with KNP-K where promoting to bishop avoids stalemate and promoting to rook or queen does not.

So there is indeed more than I could imagine. The most simple one that I had missed to find myself, even though I had already looked at KNP-K positions, was this one where only promoting to a KBN-K ending is successful:
6r1/5P2/8/4KN1k/8/8/8/8 w - - 0 1

So I learned a bit, again. Somehow I must have missed that thread from last October.

Sven

[bob]

Hi,

I was wondering: do the piece-types to what you promote a pawn to also have some specific value? Or is it the same value a piece has in general?
e.g. normally queen 9, rook 5
or is it totally depending on the situation?

I think the obvious value for a promotion is "promote-to - one pawn". For a queen, that is +8.00... You lose a pawn and gain a queen, which is a +8 transaction. If you first subtract the value of the pawn, and then add in the promotion value, then +9 would be the right value. +8 is more efficient however.