Doubled Pawn

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A Pawn is doubled (or, sad to say, tripled) if there are more pawns of the same color on a given file. Early programs and papers advocated evaluation it as half a pawn, today the penalty uses to be less severe.

It might be argued that, given a perfect pawn structure evaluation, a term such as doubled pawns would not be needed, since they usually introduce another pawn structure weaknesses: some kind of backwardness, lack of a candidate passer that otherwise would be there etc. However, most evaluation functions do not go into such details as to justify removing this term.

Types of Doubled Pawns

Hans Berliner characterizes doubled pawns by their exchange potential against opponent pawns on adjacent files [1][2]:

The doubled pawns on the b-file are the best situation, the f-file pawns are next. The h-file pawns are the worst situation because two pawns are held back by one opposing pawn, so the second pawn has little value.

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Crippled Majority

A doubled pawn of a so called "crippled" majority devalue that majority. Hans Berliner on following position in Some Innovations Introduced by Hitech [3]:

Our pawn-structure algorithm is quite simple, detecting only isolated and multiple Pawns, and the effect of multiple Pawns on viable pawn majorities. For instance, in Diagram 1 the value of White's doubled Pawn is negligible, while Black's is almost full-valued. This distinction, an innovation, was first introduced in Patsoc [4], and we were able to adapt the code to make up tables to be loaded into six identical hardware units computing pawn structure in parallel.

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