I'm implementing yet-another chess engine and i've finally gone to the dark side, having fully embraced bitboards!.
There are many new coding techniques to take advantage of and to support this I have been doing some research on how various eval elements are measured.
Regarding "doubled pawns", I found some inconsistencies regarding the definitions and the examples.
It seems the general definition is two pawns of the same color on the same file. This is how most authors describes it in most cases, but when they show examples, they always show the pawns adjacent to each other, rank-wise, such as d3 and d4.
ok, so pawns on d3 and d4 qualify, but do pawns on d3 and d5 as doubled? what if there is an intervening piece between them? still considered doubled?
what if there are 3 empty squares between them?
Exhibit A: https://chessprogramming.wikispaces.com/Doubled+Pawn
the examples only show pawns that are adjacent.