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Backward Pawn

GerdIsenberg — Fri, 05 May 2017 10:30:24 GMT

Home * Evaluation * Pawn Structure * Backward Pawn

		A backward pawn is a pawn no longer defensible by own pawns and whose stop square lacks pawn protection but is controlled by a sentry. Thus, don't considering piece tactics, the backward pawn is not able to push forward without being lost, even establishing an opponent passer. If two opposing pawns on adjacent files in knight distance are mutually backward, the more advanced is not considered backward. A backward pawn is worse, or even a real Straggler, if on a half-open file as suitable target of opponent rooks. As pointed out by Sam Hamilton ^[1], considering stop squares might be insufficient for pawns which may actually push, but have a permanent weakened telestop. On the other hand, such a backward prospective pawn has a vital tempo, which is often decisive in certain pawn endings.
Behindhand Pawn ^[2]

Publications

Hans Kmoch (1959, 1990). Pawn Power in Chess. New York: Dover, 1990. Previous ed.: New York: McKay, 1959. ISBN 0-486-26486-6

Forum Posts

2000 ...

WHAT is the definition of a backward pawn? by Bas Hamstra, CCC, December 23, 2002
Backward Pawns by Mark Lefler, CCC, March 24, 2008
Doubled and Backward Pawn Engine "Definitions" by Brian Richardson, CCC, September 07, 2009
Re: Doubled and Backward Pawn Engine "Definitions" by Sam Hamilton, CCC, September 13, 2009

2010 ...

backward pawns in Stockfish by Marek Kwiatkowski, CCC, July 16, 2010
What is a backward pawn? by Lyudmil Tsvetkov, CCC, May 12, 2014
Pawn backwardness by Natale Galioto, CCC, October 06, 2015

External Links

Backward Pawn from Wikipedia

References

^ Re: Doubled and Backward Pawn Engine "Definitions" by Sam Hamilton, CCC, September 13, 2009
^ Chess painting in oil on canvas by Elke Rehder

What links here?

Page	Date Edited
Alarm	Jun 7, 2017
Backward Pawn	May 5, 2017
Backward Pawns (Bitboards)	May 5, 2017
Bas Hamstra	Feb 4, 2018
Blockage Detection	Oct 19, 2017
Cheese	Feb 17, 2018
Cheops (Miller)	Jan 13, 2017
ChessBrainVB	Jun 24, 2017
Clarabit	Nov 3, 2011
Coiled	Mar 12, 2017
Dartmouth CP	Jan 19, 2018
Defenchess	Mar 18, 2018
Diablo	May 17, 2016
Donna	Aug 17, 2017
Doubled Pawn	Mar 27, 2017
Evaluation function draft	Jul 11, 2014
Evaluation Overlap	Jul 19, 2016
Exacto	Oct 3, 2015
Faker	Nov 11, 2017
Garbochess	Sep 23, 2017
GopherCheck	Feb 3, 2017
Hakkapeliitta	Apr 26, 2016
Hans Kmoch	Nov 11, 2017
Hidden Passed Pawn	Nov 11, 2017
Holes	Oct 16, 2017
ISA	Apr 2, 2018
Isolated Pawn	Nov 18, 2012
Kaissa	Apr 9, 2018
King Pawn Tropism	Sep 1, 2014
Lyudmil Tsvetkov	Mar 28, 2018
Marek Kwiatkowski	Oct 22, 2017
Mark Lefler	Nov 23, 2017
Minority Attack	Jun 6, 2012
Nebula	Feb 7, 2015
NoonianChess	Jan 7, 2016
Open Pawns (Bitboards)	Aug 24, 2017
Pawn chain	Jan 17, 2018
Pawn Endgame	Oct 11, 2017
Pawn Majority	Jun 8, 2012
Pawn Rams (Bitboards)	Nov 11, 2017
Pawn Structure	Oct 2, 2017
Pawns and Files (Bitboards)	Jan 16, 2013
Prédateur	Nov 11, 2016
RattateChess	Dec 2, 2014
RuyDos	Feb 17, 2018
Sam Hamilton	Jan 28, 2015
Shield	May 17, 2017
Simplex	Mar 6, 2016
Sloppy	Sep 17, 2016
Stockfish	Apr 7, 2018
Tucano	Dec 16, 2017
Vajolet	Jan 25, 2018
Wasp	Nov 24, 2017
Weak Pawns	Dec 19, 2013
Wing	Oct 26, 2017
Winglet	Apr 26, 2015

Up one level

Candidate Passed Pawn

GerdIsenberg — Sat, 11 Nov 2017 09:32:23 GMT

Home * Evaluation * Pawn Structure * Candidate Passed Pawn

		Candidate passed pawn, a pawn on a half-open file, which, if the board had only pawns on it, would eventually become a passed pawn by moving forward. Whereas this definition is obvious for a human, in a form presented above it would require no less than a separate recursive search routine. For that reason, computers have to use approximations of that rule. One possibility is to define a pawn as a candidate, if no square on its path is controlled by more enemy pawns than own pawns. However, this simple heuristics rules out an early recognition of a candidate passed pawns. For example with white pawns on a4 and b5 and black pawn on a7, the b5 pawn would be viewed as a candidate passer only after a4-a5.
White and Black candidates (b5, g5)

Forum Posts

How to define a candidate passer by Jan Willem de Kort, CCC, January 03, 2006
Outside passer and candidate passer: definition wanted! :-) by Alessandro Scotti, CCC, February 27, 2006
Improving evaluation of passed pawns by Ben-Hur Carlos Vieira Langoni Junior, CCC, January 22, 2011 » Passed Pawn

External Links

References

^ Hans Kmoch (1959, 1990). Pawn Power in Chess. New York: Dover, 1990. Previous ed.: New York: McKay, 1959. ISBN 0-486-26486-6

What links here?

Page	Date Edited
More Links
Alessandro Scotti	Feb 27, 2014
Ben-Hur Carlos Vieira Langoni Junior	Dec 17, 2013
Bismark	Apr 22, 2015
Candidate Passed Pawn	Nov 11, 2017
Candidates (Bitboards)	Nov 11, 2017
Chexa	Feb 18, 2014
Clarabit	Nov 3, 2011
Coiled	Mar 12, 2017
Dartmouth CP	Jan 19, 2018
Dictionary	Aug 24, 2017
Doubled Pawn	Mar 27, 2017
Faker	Nov 11, 2017
Garbochess	Sep 23, 2017
Hans Kmoch	Nov 11, 2017
Hidden Passed Pawn	Nov 11, 2017
ISA	Apr 2, 2018
Nebula	Feb 7, 2015
Open Pawns (Bitboards)	Aug 24, 2017
Outside passed pawn	Jun 7, 2012
Passed Pawn	Oct 11, 2017

Up one Level

Connected Passed Pawns

GerdIsenberg — Fri, 27 Mar 2015 19:27:45 GMT

Home * Evaluation * Pawn Structure * Passed Pawn * Connected Passed Pawns

Connected Passed Pawns,
two or more passed pawns on adjacent files, either as duo mutually protecting their stop squares, or as protected passed pawn defended by the second passer, may advance in tandem and are more difficult to blockade than isolated passers. In a chain they may be best countered by a bishop blocking or controlling their stop squares. The opponent king can also hold the chain on both stop squares, but is often obligated to stay inside the square of the more advanced peak. Connected passers are in particularly strong in rook endgames, but may be worse than two distant isolated passers in pawn endgames ^[1].

Forum Posts

WAC.002 by evaluation? by Luca Hemmerich, CCC, April 18, 2010 » Win at Chess
Improving SF passer code by Lyudmil Tsvetkov, CCC, March 26, 2015 » Stockfish

External Links

References

^ Re: passed pawn evaluation by Robert Hyatt, CCC, January 12, 2004

What links here?

Page	Date Edited
Amyan	Dec 10, 2013
Bishops of Opposite Colors	Aug 22, 2012
Blockade of Stop	Oct 11, 2016
Cheese	Feb 17, 2018
Chunker	Jul 12, 2016
Connected Passed Pawns	Mar 27, 2015
Luca Hemmerich	Jun 19, 2017
Outside passed pawn	Jun 7, 2012
Passed Pawn	Oct 11, 2017
Pawn Endgame	Oct 11, 2017
Protected Passed Pawn	Jun 7, 2012
Shield	May 17, 2017
Stockfish	Apr 7, 2018
Tucano	Dec 16, 2017
Win at Chess	Sep 25, 2017
Wing	Oct 26, 2017
Zurichess	Mar 12, 2018

Up one Level

Control of Stop and Telestop

GerdIsenberg — Tue, 26 Feb 2013 14:54:33 GMT

Home * Evaluation * Pawn Structure * Passed Pawn * Control of Stop and Telestop

Control of Stop and Telestop,
an evaluation feature considering square control of passed pawn's front spans, their stop and telestops including promotion square. Specially in late endgames, if the opponent king is outside the square of a passer, it might be decisive for the opponent to control the stop or at least one telestop with a piece to dynamically prevent the passer from further advancement or even queening, or to blockade the stop in time. While rooks (and queens) may control the front span indirectly from behind as considered by the Tarrasch rule, light pieces require direct control of the front span. If stops and telestops are not yet directly controlled, one may even apply fill-algorithms to determine sets of squares controlled in one move, to look whether they intersect the telestops.

What links here?

Page	Date Edited
Blockade of Stop	Oct 11, 2016
Control of Stop and Telestop	Feb 26, 2013
Mobility	Jan 17, 2018
Passed Pawn	Oct 11, 2017
Rodent	Jan 11, 2018
Spector	Nov 11, 2016
Square Control	Sep 15, 2016

Up one Level

Doubled Pawn

GerdIsenberg — Mon, 27 Mar 2017 14:06:49 GMT

Types of Doubled Pawns

Crippled Majority

All About Doubled Pawns

Home * Evaluation * Pawn Structure * Doubled Pawn

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.`
8/1p6/p3pp1p/8/8/1PP2P1P/1P3P1P/8 w - -

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.`
8/1pp2ppp/1p6/8/8/5P2/PPP2PPP/8 w - -

All About Doubled Pawns

The vast amount of detailed knowledge about doubled pawns, which rarely gets implemented, can be found in the article All About Doubled Pawns by Larry Kaufman ^[5].

Publications

Larry Kaufman (2005). All About Doubled Pawns. (first published in Chess Life, May 2005, p.22)

Forum Posts

Doubled and Backward Pawn Engine "Definitions" by Brian Richardson, CCC, September 07, 2009
passed but doubled pawns by Jon Dart, CCC, June 15, 2015 » Passed Pawn
Doubled pawns by Stefano Gemma, CCC, May 11, 2016

External Links

Doubled Pawn from Wikipedia
All About Doubled Pawns by IM Larry Kaufman
Doubled Pawns Strength and weakness by Georgi Orlov
Ástor Piazzolla - Tristezas de un Doble A, Montreux Jazz Festival, 1985 YouTube Videos

References

^ Hans Berliner (1999). The System: A World Champion's Approach to Chess, Gambit Publications, ISBN 1-901983-10-2
^ Types of doubled pawns from Wikipedia
^ Hans Berliner (1987). Some Innovations Introduced by Hitech. ICCA Journal, Vol. 10, No. 3, pp. 111-117
^ Hans Berliner (1985). Computer Chess at Carnegie Mellon University. Advances in Computer Chess 4
^ Larry Kaufman (2005). All About Doubled Pawns. (first published in Chess Life, May 2005, p.22)

What links here?

Page	Date Edited
More Links
Alarm	Jun 7, 2017
Amyan	Dec 10, 2013
Applied Concepts	Dec 25, 2017
Bismark	Apr 22, 2015
Cheese	Feb 17, 2018
Cheops (Miller)	Jan 13, 2017
chess22k	Apr 23, 2018
ChessBrainVB	Jun 24, 2017
Clarabit	Nov 3, 2011
Coiled	Mar 12, 2017
Cyrus	Jul 22, 2014
Dartmouth CP	Jan 19, 2018
Defenchess	Mar 18, 2018
Diablo	May 17, 2016
Dispersion and Distortion	Nov 11, 2017
Donna	Aug 17, 2017
Dorpsgek	Apr 2, 2018
Double and Triple (Bitboards)	May 12, 2016
Doubled Pawn	Mar 27, 2017
Eval Tuning in Deep Thought	Jun 7, 2016
Evaluation function draft	Jul 11, 2014
Evaluation Overlap	Jul 19, 2016
Exacto	Oct 3, 2015
Garbochess	Sep 23, 2017
Gk	Oct 9, 2017
Gogobello	Jul 30, 2017
GopherCheck	Feb 3, 2017
Hakkapeliitta	Apr 26, 2016
Hans Kmoch	Nov 11, 2017
ISA	Apr 2, 2018
Kaissa	Apr 9, 2018
Larry Kaufman	Jan 28, 2018
Marvin	Feb 10, 2018
Nebula	Feb 7, 2015
Neurosis	Dec 23, 2017
Passed Pawn	Oct 11, 2017
Patsoc	Jan 7, 2016
Paul	Jan 8, 2016
Pawn Center	Feb 12, 2015
Pawn Majority	Jun 8, 2012

Up one Level

Duo Trio Quart (Bitboards)

GerdIsenberg — Fri, 18 Aug 2017 17:28:27 GMT

Home * Board Representation * Bitboards * Pawn Pattern and Properties * Duo Trio Quart

Pawn-Duo, (Phalanx) ^[1]
two adjacent pawns of the same color on the same rank that mutually cover the other's stop square. A Trio are three horizontal friendly pawns, a Quart four horizontal friendly pawns.

Working in the bitboard centric world to determine pawn related pattern set-wise.

The code snippets rely on shifting bitboards, specially by one step only.

Neighbors

To get pawns with east or west neighbors is simple:

U64 pawnsWithEastNeighbors(U64 pawns) {
   return pawns & westOne (pawns);
}
 
U64 pawnsWithWestNeighbors(U64 pawns) {
   return pawnsWithEastNeighbors(pawns) << 1; // * 2
}

U64 pawnsWithWestNeighbors(U64 pawns) {
   return pawns & eastOne (pawns);
}
 
U64 pawnsWithEastNeighbors(U64 pawns) {
   return pawnsWithWestNeighbors(pawns) >> 1;
}

pawns               pawns with east     pawns with west     pawns with east
                    neighbors           neighbors           and west neighbors
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
1 1 1 . . . . .     1 1 . . . . . .     . 1 1 . . . . .     . 1 . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
. . . . . 1 1 .     . . . . . 1 . .     . . . . . . 1 .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .

Neighbor Algebra

Pawns with east or west neighbors are at least member of a duo. Pawns with east and west neighbors at least member of a trio. If two neighbors have both east and west neighbors, it is at least a quart.

An exclusive pawn duo is therefor a pawn with one neighbor, while this neighbor has no other neighbor as well.

U64 duo (U64 pawns) {
   U64 withWestNeighbors = pawnsWithWestNeighbors(pawns);
   U64 withEastNeighbors = withWestNeighbors >> 1;
 
   U64 withOneExclusiveNeighbor  = withWestNeighbors ^ withEastNeighbors;
   U64 withExclusiveWestNeighbor = withWestNeighbors & withOneExclusiveNeighbor;
   U64 withExclusiveEastNeighbor = withEastNeighbors & withOneExclusiveNeighbor;
 
   U64 duoWestOne = withEclusiveEastNeighbor & (withEclusiveWestNeighbor >> 1);
   U64 duoEastOne = duoWestOne << 1;
   return duoWestOne | duoEastOne;
}

pawns               pawns with excl.    pawns with excl.    duo
                    east neighbor       west neighbor
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
1 1 1 . . . . .     1 . . . . . . .     . . 1 . . . . .     . . . . . . . .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .
. . . . . 1 1 .     . . . . . 1 . .     . . . . . . 1 .     . . . . . 1 1 .
. . . . . . . .     . . . . . . . .     . . . . . . . .     . . . . . . . .

Forum Posts

The phalanx concept by Lyudmil Tsvetkov, CCC, May 21, 2014

External Links

Pawn Structure (General) | Page 5 of 5 | Phalanx Formation
Duet from Wikipedia
Phalanx from Wikipedia
Trio from Wikipedia
Kinga Głyk Trio - Walking Baby, VisionInMusica, Terni, March 10, 2017, YouTube Video
Kinga Głyk, Irek Głyk, Rafal Stepien
Quart (disambiguation) from Wikipedia
Panta Rhei plays Bartók's Quarts, 1977, YouTube Video

References

^ Pawn Structure (General) | Page 5 of 5 | Phalanx Formation

What links here?

Page	Date Edited
Backward Pawns (Bitboards)	May 5, 2017
ChessBrainVB	Jun 24, 2017
Connected Passed Pawns	Mar 27, 2015
Dartmouth CP	Jan 19, 2018
Demolito	Mar 1, 2018
Design Principles	Jan 17, 2018
Duo Trio Quart (Bitboards)	Aug 18, 2017
En prise	Oct 11, 2016
GopherCheck	Feb 3, 2017
Hanging pawns	Aug 5, 2015
Hanging Piece	Jan 14, 2017
Hans Kmoch	Nov 11, 2017
Isolated Pawns (Bitboards)	Nov 18, 2012
Kaissa	Apr 9, 2018
Lyudmil Tsvetkov	Mar 28, 2018
Pawn Pattern and Properties	Nov 11, 2017
Pawn Structure	Oct 2, 2017
Pawns Breakthrough	May 4, 2014
Protected Passed Pawn	Jun 7, 2012
Stockfish	Apr 7, 2018

Up one Level

Faker

GerdIsenberg — Sat, 11 Nov 2017 09:14:51 GMT

Home * Evaluation * Pawn Structure * Faker

		Faker, a "faked" candidate with more opponent sentries than own helpers ^[1] ^[2]. The opponent sentries control the stop square (or tele-stop) of the faker, while the helpers defend the appropriate squares. If the number of helpers becomes equal (for instance due to a pawn-capture) the faker becomes a real candidate. A faker should not receive a candidate bonus, but is not that bad as a backward pawn. Also two opponent sentries which control the same stop square, leave a hole between both sentries, which might be considered elsewhere.
Faker c4, two sentries, but only one helper

External Links

Pawn Power in Chess by Hans Kmoch - Glossary of Terms - Chess Forums - Chess.com

Fake

Fake News

References

^ Hans Kmoch (1959, 1990). Pawn Power in Chess. New York: Dover, 1990. Previous ed.: New York: McKay, 1959. ISBN 0-486-26486-6
^ Pawn Power in Chess by Hans Kmoch - Glossary of Terms - Chess Forums - Chess.com

What links here?

Page	Date Edited
Backward Pawn	May 5, 2017
Backward Pawns (Bitboards)	May 5, 2017
Candidate Passed Pawn	Nov 11, 2017
Candidates (Bitboards)	Nov 11, 2017
Coiled	Mar 12, 2017
Dictionary	Aug 24, 2017
Faker	Nov 11, 2017
Hidden Passed Pawn	Nov 11, 2017
Pawn Structure	Oct 2, 2017

Up one Level

Hanging pawns

GerdIsenberg — Wed, 05 Aug 2015 21:42:03 GMT

The Hanging Pawns formation

See also

External Links

What links here?

Home * Evaluation * Pawn Structure * Hanging pawns

Hanging pawns are an open, half-isolated duo. It means that they are standing next to each other on the adjacent half-open files, usually on the fourth rank, mutually protecting their stop squares. They share a number of characteristics of weak pawns - they are not directly protected by other pawns and may become targets of attack - but unlike them they have dynamic potential of executing a pawn breakthrough and thus creating a passed pawn (admittedly being an isolated pawn at the same time). The side with hanging pawns also tends to enjoy a space advantage.

The term "hanging" in chess otherwise refers attacked to undefended pieces en prise.

The Hanging Pawns formation

8/pp3ppp/4p3/8/2PP4/8/P4PPP/8 w - -

Most of the programs do not have a special evaluation of hanging pawns, relying on search to decide if they are an asset or a liability in a given position.

External Links

The Queen's Gambit - Hanging Pawns from Pawn structure at Wikipedia
Hanging Pawns, Ten Cents a Pair review by Larry Tapper from ChessCafe.com
Hanging Pawns from chessgames.com
The Lounge Lizards - Snakes Can´t Sleep (the hanging), Jazz Gipfel 89, Liederhalle, Stuttgart, July 22, 1989, YouTube Video

What links here?

Page	Date Edited
Connected Passed Pawns	Mar 27, 2015
Dictionary	Aug 24, 2017
Duo Trio Quart (Bitboards)	Aug 18, 2017
En prise	Oct 11, 2016
Hanging pawns	Aug 5, 2015
Hanging Piece	Jan 14, 2017
Isolated Pawns (Bitboards)	Nov 18, 2012
Pawn Structure	Oct 2, 2017
Weak Pawns	Dec 19, 2013

Up one Level

Hidden Passed Pawn

GerdIsenberg — Sat, 11 Nov 2017 09:25:01 GMT

Sample

Comparison with Candidates

See also

References

What links here?

Home * Evaluation * Pawn Structure * Hidden Passed Pawn

The Hidden Passed Pawn is an evaluation term used in Crafty, in the terminology proposed by Hans Kmoch it is referred to as a Sneaker ^[1] ^[2]. It is a rammed pawn already on the opponent side of the board without further sentries, which may become a passer through a sacrificial combination usually by a faker, which possibly allows the opponent to establish a passer as well, though at least two ranks less advanced and losing the pawn race assuming both unstoppable.

Sample

Suppose that white has pawns on a6 and b5, and black on a7. At first glance we have a backward pawn on b5, which is bad for white. However, after playing b5-b6, white gets a passed pawn either there or on a6. For that reason the pawn on a6 should be termed "a hidden passed pawn" and awarded a bonus if "unstoppable".

Fakers on b5 and g4 make a6 and h5 Sneakers

Comparison with Candidates

If we put the sneakers of the above position one rank back so that they become helpers of the now neighbored candidates, the usual idea is to advance the candidates instead of the helpers. The lonesome sentry, forced to capture, may be recaptured to establish an exclusive passer on the candidate's file. Alternatively instead of the recapture, the helper may advance to become a passer as well, which yields to a transposition of the hidden passed pawn idea. This may be stronger if the pawn becomes an unstoppable passer leaving the opponent king outside its square, while the candidate could be caught.

a5 or b5?

References

^ Hans Kmoch (1959, 1990). Pawn Power in Chess. New York: Dover, 1990. Previous ed.: New York: McKay, 1959. ISBN 0-486-26486-6
^ Pawn Power in Chess by Hans Kmoch - Glossary of Terms - Chess Forums - Chess.com

What links here?

Page	Date Edited
Amundsen	Sep 3, 2013
Backward Pawn	May 5, 2017
Backward Pawns (Bitboards)	May 5, 2017
Candidate Passed Pawn	Nov 11, 2017
Candidates (Bitboards)	Nov 11, 2017
Coiled	Mar 12, 2017
Dictionary	Aug 24, 2017
Hans Kmoch	Nov 11, 2017
Hidden Passed Pawn	Nov 11, 2017
Passed Pawn	Oct 11, 2017
Passed Pawns (Bitboards)	Aug 23, 2010
Pawn Endgame	Oct 11, 2017
Pawn Structure	Oct 2, 2017
Unstoppable Passer	Jun 21, 2016

Up one Level

Holes

GerdIsenberg — Mon, 16 Oct 2017 19:42:41 GMT

Home * Evaluation * Pawn Structure * Holes

		Holes, squares that cannot be possibly covered by own pawns, usually also controlled by the enemy pawns. A typical example is d4 square after White forms a triangle consisting of pawns on c4, d3 and e4. Holes are excellent locations for enemy minor pieces, safer than outposts. For that reason one should keep minor pieces to cover the holes in one's position. Along with bitboard pawn patterns, holes may be determined by the relative complement of front attack spans usually restricted to the area of the own 3rd and 4th rank of the extended center.
Simulated view of a black hole ^[1]

Forum Posts

Pawn Structure "Holes" and Move Ordering by Daniel A. Thies in rgcc February 12, 1996 » Move Ordering
Re: Did Cray Blitz really have a win? by Robert Hyatt, rec.games.chess.misc, March 12, 1999 » ACM 1985, WCCC 1986, Cray Blitz

External Links

References

^ Simulated view of a black hole (center) in front of the Large Magellanic Cloud. Note the gravitational lensing effect, which produces two enlarged but highly distorted views of the Cloud. Across the top, the Milky Way disk appears distorted into an arc. Image by Alain r, September 08, 2006 CC BY-SA 2.5, Wikimedia Commons

What links here?

Page	Date Edited
ACM 1985	Jun 21, 2017
Blockade of Stop	Oct 11, 2016
CC Sapiens	Oct 29, 2014
Cray Blitz	Dec 25, 2017
Dartmouth CP	Jan 19, 2018
Demolito	Mar 1, 2018
Faker	Nov 11, 2017
Fianchetto	Feb 18, 2015
Holes	Oct 16, 2017
Move Ordering	Feb 27, 2018
Outposts	Apr 24, 2017
Pawn Structure	Oct 2, 2017

Up one Level

Isolated Pawn

GerdIsenberg — Sun, 18 Nov 2012 10:38:41 GMT

Home * Evaluation * Pawn Structure * Isolated Pawn

		Isolated Pawn, a pawn with no pawns of the same color on the neighboring files. It is usually evaluated just like a backward pawn, except the penalty tends to be bigger, as it is more open to attacks. It may be considered even weaker if positioned on the half-open file, as then it is open to attack by enemy rooks. Many programs tend to evaluate an isolated pawn in the center as weaker than on the wing, as it can be attacked from more directions ^[1].
Isolated Pawn by Elke Rehder ^[2]

Examples

There is a whole class of openings characterized by the presence of an isolated queen's pawn. In exchange for this structural weakness the side with an IQP gets greater mobility, therefore this kind of positions can be used for balancing the evaluation functions parameters.

External Links

References

^ Re: Self-test and others rating stuffs... by Amir Ban, CCC, January 02, 1998
^ Chess - Isolated Pawn, chess paintings in mixed media and in watercolor © Elke Rehder

What links here?

Page	Date Edited
More Links
Alarm	Jun 7, 2017
Amyan	Dec 10, 2013
Applied Concepts	Dec 25, 2017
Cheese	Feb 17, 2018
Cheops (Miller)	Jan 13, 2017
chess22k	Apr 23, 2018
ChessBrainVB	Jun 24, 2017
Clarabit	Nov 3, 2011
Coiled	Mar 12, 2017
Cyrus	Jul 22, 2014
Dartmouth CP	Jan 19, 2018
Defenchess	Mar 18, 2018
Demolito	Mar 1, 2018
Dispersion and Distortion	Nov 11, 2017
Donna	Aug 17, 2017
Dorpsgek	Apr 2, 2018
Doubled Pawn	Mar 27, 2017
Evaluation function draft	Jul 11, 2014
Evaluation Overlap	Jul 19, 2016
Exacto	Oct 3, 2015
Garbochess	Sep 23, 2017
Gk	Oct 9, 2017
Gogobello	Jul 30, 2017
GopherCheck	Feb 3, 2017
Hakkapeliitta	Apr 26, 2016
Hanging pawns	Aug 5, 2015
Hans Kmoch	Nov 11, 2017
ISA	Apr 2, 2018
Isolated Pawn	Nov 18, 2012
Isolated Pawns (Bitboards)	Nov 18, 2012
Kaissa	Apr 9, 2018
Marvin	Feb 10, 2018
Minority Attack	Jun 6, 2012
Nebula	Feb 7, 2015
Neurosis	Dec 23, 2017
NoonianChess	Jan 7, 2016
Open Pawns (Bitboards)	Aug 24, 2017
Pawn Rams (Bitboards)	Nov 11, 2017
Pawn Structure	Oct 2, 2017
Pawns and Files (Bitboards)	Jan 16, 2013

Up one level

Isolated Pawns (Bitboards)

GerdIsenberg — Sun, 18 Nov 2012 09:53:37 GMT

Isolani by Square

Isolanis and Half-isolanis set-wise

Hanging pawns

What links here?

Home * Board Representation * Bitboards * Pawn Pattern and Properties * Isolated Pawns

An Isolated Pawn or Isolani has no friendly pawns on adjacent files .

Isolani by Square

To determine whether a pawn is isolated, we simply lookup an array with neighboring file-masks. If the intersection of neighbored files with own pawns is empty, the pawn is isolated. This symmetrical property appears to be equal for white and black pawns.

if ( (arrNeighborFiles[sqOfWhitePawn] & pawnBB[white]) == 0 ) -> pawn is isolated

arrNeighborFiles[d*]
. . 1 . 1 . . .
. . 1 . 1 . . .
. . 1 . 1 . . .
. . 1 . 1 . . .
. . 1 . 1 . . .
. . 1 . 1 . . .
. . 1 . 1 . . .
. . 1 . 1 . . .

The arrNeighborFiles might be condensed to eight bitboards only, instead of 64 - if we index by

file(sq) == sq & 7

instead of square.

Isolanis and Half-isolanis set-wise

Isolated pawns are the relative complement of pawns with the union of their own attack fills over the whole file. To keep disjoint pawns with no neighbor on either east or west adjacent files has the advantage of greater versatility. Isolanis are the intersection of them, half-isolanis the exclusive or:

U64 noNeighborOnEastFile (U64 pawns) {
    return pawns & ~westAttackFileFill(pawns);
}
 
U64 noNeighborOnWestFile (U64 pawns) {
    return pawns & ~eastAttackFileFill(pawns);
}
 
U64 isolanis(U64 pawns) {
   return  noNeighborOnEastFile(pawns)
         & noNeighborOnWestFile(pawns);
}
 
U64 halfIsolanis(U64 pawns) {
   return  noNeighborOnEastFile(pawns)
         ^ noNeighborOnWestFile(pawns);
}

Hanging pawns

Hanging pawns are a duo of open and half-isolated pawns.

U64 wHangingPawns(U64 wpawns, U64 bpawns) {
   return wOpenPawns(wpawns, bpawns)
        & halfIsolanis(wpawns) & duo(wpawns);
}

What links here?

Page	Date Edited
Attack Spans	Mar 4, 2010
Backward Pawns (Bitboards)	May 5, 2017
Dispersion and Distortion	Nov 11, 2017
En prise	Oct 11, 2016
Hanging pawns	Aug 5, 2015
Hanging Piece	Jan 14, 2017
Hans Kmoch	Nov 11, 2017
Isolated Pawn	Nov 18, 2012
Isolated Pawns (Bitboards)	Nov 18, 2012
Murka	Nov 11, 2016
Pawn Islands (Bitboards)	May 4, 2017
Pawn Pattern and Properties	Nov 11, 2017
Pawn Spans	Jul 22, 2010
Robocide	May 11, 2016
Weak Pawns	Dec 19, 2013

Up one Level

Minority Attack

GerdIsenberg — Wed, 06 Jun 2012 15:55:42 GMT

Home* Evaluation * Pawn Structure * Minority Attack

		Minority attack, a method of play typical in positions where white has pawns on a2, b2 and d4, whereas black has pawns on a7, b7, c6 and d5, the so-called Carlsbad Pawn Structure ^[1]. Despite the fact that black nominally has a pawn majority on the queenside, white attacks by moving the b-pawn forward and organizing piece pressure along the c-file. Then either white plays b5xc6, weakening black c-pawn, or black plays c6xb5, opening the c-file and isolating the d-pawn. Beside the typical heuristics considering backward and isolated pawns and rooks on open files, a possible idea to encourage a minority attack would be an additional advance bonus for pawns adjacent to half-open files, considering king safety related pawn shield issues.
The Carlsbad Pawn Structure ^[2]

Forum Posts

Minority attack: a problem even for new programs? by Dirk Frickenschmidt, CCC, October 17, 1998

External Links

References

^ Karlsbad pawn structure from Francesco Costa's web page on chess
^ The "Karlsbad" Pawn Structure (pdf)

What links here?

Page	Date Edited
Dirk Frickenschmidt	Jun 28, 2017
Mephisto Dallas	Sep 1, 2017
Minority Attack	Jun 6, 2012
N.N.	Jan 20, 2018
Pawn Majority	Jun 8, 2012
Pawn Structure	Oct 2, 2017
Planning	Feb 12, 2018
Strategy	Jan 18, 2018

Up one Level

Outside passed pawn

GerdIsenberg — Thu, 07 Jun 2012 19:02:59 GMT

Home * Evaluation * Pawn Structure * Passed Pawn * Outside Passed Pawn

The Outside Passed Pawn evaluation term used in the endgame (or just in the pawn endgame) by a couple of strong chess programs, most notably Crafty.

A Outside Passed Pawn is a passer placed on a leftmost (rightmost) file with a pawn of either color on it. All other things being equal, it constitutes almost a winning advantage. This is because it may sacrifice itself, driving the enemy king far away from its own pawns, which may be then captured by the other king.

Whereas the principle is simple, the exact implementation rules become tricky because of the numerous exceptions. Broadly speaking, this evaluation term has no use under the pawn race conditions or in positions which might possibly lead to one: if the other side has an unstoppable passed pawn, connected or protected passer, or even the strong candidate passed pawn.

Forum Posts

Outside passer and candidate passer: definition wanted! :-) by Alessandro Scotti, CCC, February 27, 2006

External Links

Outside passed pawn from Wikipedia

What links here?

Page	Date Edited
Alessandro Scotti	Feb 27, 2014
Outside passed pawn	Jun 7, 2012
Passed Pawn	Oct 11, 2017
Pawn Endgame	Oct 11, 2017
Unstoppable Passer	Jun 21, 2016

Up one Level

Passed Pawn

GerdIsenberg — Wed, 11 Oct 2017 19:22:33 GMT

Home * Evaluation * Pawn Structure * Passed Pawn

		A passed pawn, also called free pawn or passer, is a pawn with no opponent pawns in front on the same or adjacent files. In case of doubled pawns, it is wrong to score the back twin as passed, even if it meets the above conditions. Therefor, the passer requires his front span disjoint from all other pawns, as well as the front fill disjoint from opponent pawn attacks, which also excludes pawn levers ^[1]. In its simplest form, passed pawn evaluation assigns a bonus which increases as the pawn advances, often by dedicated piece-square tables. There are, however, different considerations to be taken into account, some of which are listed below.
Schachclub Freibauer Schöneberg ^[2]

Considerations

Please note that a hidden passed pawn is not a passer according to the above definition.

Forum Posts

1998 ...

Passed Pawn Evaluation by Stuart Cracraft, CCC, April 27, 1998
Passed pawn values by James Robertson, CCC, October 27, 1999

2000 ...

Passed Pawn Suite by Howard Exner, CCC, February 24, 2000 » Test-Positions
Intersting testposition: multiple passed pawns by Alexander Kure, CCC, March 23, 2003
passed pawn evaluation by macaroni, CCC, January 11, 2004

2010 ...

Passed Pawns (endgame) by Marek Kwiatkowski, CCC, May 07, 2010
An unstoppable passed pawn by Marek Kwiatkowski, CCC, June 11, 2010
Improving evaluation of passed pawns by Ben-Hur Carlos Vieira Langoni Junior, CCC, January 22, 2011 » Candidate Passed Pawn
passed pawn question by Alberto Sanjuan, CCC, August 02, 2013

2015 ...

The strongest passer by Lyudmil Tsvetkov, CCC, February 19, 2015
bad eval for passers ? by Daniel Anulliero, CCC, February 23, 2015
passed but doubled pawns by Jon Dart, CCC, June 15, 2015 » Doubled Pawn
Passed pawn detection in array based board representations by Shawn Chidester, CCC, September 20, 2015
Passed pawn evaluation by Daniel Mehrmann, CCC, December 13, 2015

External Links

References

^ passed pawn question by Alberto Sanjuan, CCC, August 02, 2013
^ Schachclub Freibauer Schöneberg e.V

What links here?

Page	Date Edited
AI Chess	Jan 7, 2016
Alarm	Jun 7, 2017
Alberto Sanjuan	Nov 3, 2014
Alex Kure	Aug 27, 2016
Amundsen	Sep 3, 2013
Amyan	Dec 10, 2013
Andscacs	Jan 16, 2018
Asymmetric evaluation	Nov 17, 2016
Backward Pawn	May 5, 2017
Ben-Hur Carlos Vieira Langoni Junior	Dec 17, 2013
Bishops of Opposite Colors	Aug 22, 2012
Bismark	Apr 22, 2015
Bison	Sep 29, 2016
Blockade	Oct 19, 2017
Blockade of Stop	Oct 11, 2016
Blockage Detection	Oct 19, 2017
Bobby	Jan 7, 2016
Bobcat	Jun 27, 2017
Brainstorm	Jun 24, 2017
Candidate Passed Pawn	Nov 11, 2017
Candidates (Bitboards)	Nov 11, 2017
Cheese	Feb 17, 2018
Chenard	Sep 5, 2015
chess22k	Apr 23, 2018
ChessBrainVB	Jun 24, 2017
Chexa	Feb 18, 2014
Chiron	Sep 24, 2017
Clarabit	Nov 3, 2011
Coiled	Mar 12, 2017
Comet	Jan 8, 2016
Connected Passed Pawns	Mar 27, 2015
Control of Stop and Telestop	Feb 26, 2013
CookieCat	Nov 15, 2016
Counter	Nov 13, 2017
CPW-Engine	Dec 31, 2014
Crafty	Jan 28, 2018
Cupcake	May 19, 2016
Daniel Mehrmann	Dec 13, 2015
Darmenios	Jan 7, 2016
Dartmouth CP	Jan 19, 2018
Defenchess	Mar 18, 2018
Delicate Brute	Jun 7, 2016
Demolito	Mar 1, 2018
Diablo	May 17, 2016
Dictionary	Aug 24, 2017
Djinn	Feb 8, 2016
Donna	Aug 17, 2017
Dorpsgek	Apr 2, 2018
Doubled Pawn	Mar 27, 2017
Endgame	Sep 18, 2017
Enigma	Feb 9, 2015
Eval Tuning in Deep Thought	Jun 7, 2016
Evaluation function draft	Jul 11, 2014
Evaluation Overlap	Jul 19, 2016
Exacto	Oct 3, 2015
Fortress (Engine)	Oct 19, 2017
Freyr	Mar 6, 2014
Garbochess	Sep 23, 2017
Gibbon	Dec 23, 2014
Gk	Oct 9, 2017
Gogobello	Jul 30, 2017
GopherCheck	Feb 3, 2017
Hakkapeliitta	Apr 26, 2016
Hanging pawns	Aug 5, 2015
Hidden Passed Pawn	Nov 11, 2017
ISA	Apr 2, 2018
IsiChess	Jan 7, 2016
Jumbo	Dec 19, 2017
Kaissa	Apr 9, 2018
King Centralization	Oct 30, 2017
King Pattern	Nov 15, 2013
King Pawn Tropism	Sep 1, 2014
Kiwi	Sep 2, 2016
Komodo	Mar 6, 2018
Ktulu	May 16, 2015
Late Move Reductions	Sep 25, 2017
Marvin	Feb 10, 2018
Maverick	Jan 7, 2016
MChess	Feb 26, 2018
Mephisto Dallas	Sep 1, 2017
Mephisto Lyon	Sep 1, 2017
Mobility	Jan 17, 2018
Nebula	Feb 7, 2015
Neurosis	Dec 23, 2017
NG-play	Feb 26, 2017
Nimzo	Dec 30, 2017
Nirvanachess	Sep 30, 2017
NoonianChess	Jan 7, 2016
OliThink	May 19, 2017
Open Pawns (Bitboards)	Aug 24, 2017
Oracle	Sep 4, 2016
Orion	Oct 15, 2017
Ostrich	Dec 28, 2017
Outside passed pawn	Jun 7, 2012
Passed Pawn	Oct 11, 2017
Passed Pawn Extensions	May 11, 2015
Passed Pawns (Bitboards)	Aug 23, 2010
Patzer	Apr 5, 2017
Pawn Endgame	Oct 11, 2017
Pawn Hash Table	Feb 1, 2018
Pawn Majority	Jun 8, 2012
Pawn Structure	Oct 2, 2017
PawnKing	Sep 5, 2014
Pawns Breakthrough	May 4, 2014
Peasant	May 21, 2015
Point Value by Regression Analysis	Aug 26, 2017
PolarChess	May 15, 2017
Prédateur	Nov 11, 2016
Protected Passed Pawn	Jun 7, 2012
RattateChess	Dec 2, 2014
Rebel	Feb 25, 2018
RedQueen	Nov 13, 2017
Réti Endgame Study	Feb 25, 2014
Rhetoric	Nov 15, 2017
Robocide	May 11, 2016
Rodent	Jan 11, 2018
Rule of the Square	Sep 6, 2014
RuyDos	Feb 17, 2018
Sayuri	Oct 1, 2017
Scorpio	Mar 28, 2018
SCP	Jun 16, 2016
Sentry	Nov 11, 2017
Shield	May 17, 2017
Simplex	Mar 6, 2016
Sloppy	Sep 17, 2016
Spector	Nov 11, 2016
Square Control	Sep 15, 2016
Stockfish	Apr 7, 2018
Tactics	Jan 12, 2018
Tarrasch Rule	Jun 2, 2014
Teki	Mar 29, 2018
Test-Positions	Feb 25, 2018
Texel	Oct 9, 2017
Thor's Hammer	Nov 23, 2013
Tucano	Dec 16, 2017
Unstoppable Passer	Jun 21, 2016
Vajolet	Jan 25, 2018
Vice	Mar 8, 2016
Wasp	Nov 24, 2017
WChess	Jan 7, 2016
Wing	Oct 26, 2017
Winglet	Apr 26, 2015
Witz	Nov 14, 2017
WyldChess	Mar 10, 2018
Xiphos	Apr 22, 2018
Xpdnt	Sep 13, 2015
Zeus RU	Jun 6, 2015
Zurichess	Mar 12, 2018

Up one Level

Pawn Center

GerdIsenberg — Thu, 12 Feb 2015 10:50:48 GMT

Home * Evaluation * Pawn Structure * Pawn Center

Chess theory holds that it is advantageous to control the center with pawns. This principle has been stressed especially in the classical period of chess theory to the extent that some perfectly healthy openings were considered disadvantageous on the grounds that they "give up the center" like the Rubinstein line in the French. Many of the hypermodern openings adopt the opposite attitude, allowing the opponent to build the pawn center in order to attack it later on. It follows that the evaluation function, in order to remain flexible, should not assign too great weights to pawn center - else it would be unable to evaluate this kind of position correctly.

Terms

related to Pawn Center by Hans Kmoch ^[1] ^[2]

Center lever - A lever wholly within the two center files
Center pawn - Pawn on the d- or e-file
Centerswap - A capture from and to the d- or e-file that produces a doubled pawn
Innerswap - A capture towards the center that produces a doubled pawn

Coding

Coding pawn center evaluation routine, one can

use values in a piece-square table for pawns
raise the material value of central pawns or
assign bonuses for certain pawn configurations, like the following:
- ideal formation of white pawns on d4 and e4
- good formation of white pawns on d4 and c4
- e4 or d4 pawn defended by another one

Some other evaluation factors are interrelated with the pawn center, like the penalty for a knight on c3 blocking c2 pawn in the closed openings.

Forum Posts

Why a Pawn Center? by Laurence Chen, CCC, January 20, 1999
Closed pawn center and Kingsafety by Gerd Isenberg, CCC, March 05, 2004
Pawn checks and center levers by Lyudmil Tsvetkov, CCC, February 11, 2015

External Links

References

^ Glossary for Pawn Power In Chess by Hans Kmoch
^ Hans Kmoch (1959, 1990). Pawn Power in Chess. New York: Dover, 1990. Previous ed.: New York: McKay, 1959. ISBN 0-486-26486-6, Google Books, amazon

What links here?

Page	Date Edited
Alarm	Jun 7, 2017
Amyan	Dec 10, 2013
Center	Jun 21, 2016
Center Control	Jan 17, 2018
Evaluation of Pieces	Jan 8, 2018
Evaluation Patterns	Jun 24, 2013
Hans Kmoch	Nov 11, 2017
Kaissa	Apr 9, 2018
Opening	Jun 25, 2017
Ostrich	Dec 28, 2017
Pawn Center	Feb 12, 2015
Pawn Pattern and Properties	Nov 11, 2017
Pawn Structure	Oct 2, 2017
Strategic Test Suite	Dec 19, 2016

Up one Level

Pawn chain

GerdIsenberg — Wed, 17 Jan 2018 18:12:37 GMT

Home * Evaluation * Pawn Structure * Pawn chain

A Pawn chain consists of pawns placed on the same diagonal, without interruption, so that only one of them is undefended. That pawn is called a base of pawn chain. The player opposing the pawn chain should attack its base or else strive to exchange pawns being parts of the chain. The old chess theory warned against attacking the peak of the chain, but some lines of the French defense show that this strategy is perfectly applicable.

Chain Direction

As pointed out by Lyudmil Tsvetkov, the direction of a rammed pawn at least triple chain with its peak pretends the wing concerning piece attacks and king safety issues ^[1]. In the left diagram, omitting pieces but assuming middlegame, the black king should receive a penalty, in the color flipped position on the right, the white king accordantly ^[2]:


6k1/5p2/4p3/3pP3/2pP4/2P5/8/6K1 w - -		6k1/8/2p5/2Pp4/3Pp3/4P3/5P2/6K1 b - -

Further, an open backward straggler is a weak base of the chain.

Forum Posts

2014

5 underestimated evaluation rules by Lyudmil Tsvetkov, CCC, January 23, 2014
Huge simplification by Lyudmil Tsvetkov, CCC, April 25, 2014 » Stockfish
Re: Huge simplification by Lyudmil Tsvetkov, CCC, April 26, 2014
Re: Huge simplification by Lyudmil Tsvetkov, CCC, April 26, 2014

2015

LCP by Lyudmil Tsvetkov, CCC, February 09, 2015
pointy chains redux (part 1) by Carl Langan, CCC, February 20, 2015
Longer chain pawn again by Lyudmil Tsvetkov, CCC, February 25, 2015
pattern coding in bitboards by Pawel Koziol, CCC, February 26, 2015 » Defended Defenders
Chain, duo, connected by Lyudmil Tsvetkov, CCC, May 02, 2015

External Links

References

^ Re: Huge simplification by Lyudmil Tsvetkov, CCC, April 26, 2014
^ Re: Huge simplification by Lyudmil Tsvetkov, CCC, April 26, 2014

What links here

Page	Date Edited
Connected Passed Pawns	Mar 27, 2015
Connectivity	Mar 6, 2016
Dartmouth CP	Jan 19, 2018
Defended Pawns (Bitboards)	Feb 27, 2015
Exacto	Oct 3, 2015
Fortress	Feb 1, 2018
GopherCheck	Feb 3, 2017
King Safety	Feb 14, 2018
Lyudmil Tsvetkov	Mar 28, 2018
Nirvanachess	Sep 30, 2017
Pawel Koziol	Dec 17, 2017
Pawn chain	Jan 17, 2018
Pawn Structure	Oct 2, 2017
Rook on Open File	Apr 24, 2017
Space	Jan 18, 2018
Stockfish	Apr 7, 2018
Vajolet	Jan 25, 2018

Up one Level

Pawn Hash Table

GerdIsenberg — Thu, 01 Feb 2018 19:21:26 GMT

Home * Evaluation * Pawn Structure * Pawn Hash Table

		A Pawn Hash Table is often used inside a chess programs to cache purely pawn related pattern and evaluation stuff. Compared to the main transposition table, since the pawn structure inside the search changes rarely or transpose, the number of cached entries required might be quite low (a few K) to get a sufficient hit rate above 95% or even 99% for most positions, specially if the pawn structure is settled or relatively fixed after the opening. On the other hand, most programmers store not only pure aggregated pawn evaluation scores, but other computation expensive pawn structure stuff which is used in second pass evaluation considering pieces and king. Terms for various game phases and king origins for all possible wings/center per side are often calculated speculatively, i.e. pawn shield or pawn storm stuff later used by king safety. While the content of the pawn hash table entry varies a lot between different chess programs and their implementation, it is not uncommon that one entry exceeds 1/2 K-Byte. Some programs store sets or bitboards of strong pawns (passers, candidates), square of most advanced passer, different kind of weak pawn sets and whatever else. Despite, some programs cache pawn-king stuff separately which requires king squares included inside the index calculation as well table entry for verifications.
Pawns threaten the King ^[1]

Pawn Hash Index

Most simple, common and recommend is to keep an incremental updated, dedicated Zobrist- or BCH-keys similar to the main transposition table, initialized from all squares occupied by pawns only, side to move does not matter. The update of that key is therefor only necessary for the relative rare pawn moves or captures with pawns as aggressor or victim. The hash table index is computed by key modulo number of entries, which might be a cheap and-instruction from the key for power of two sized tables.

Alternatively, considering hits from the transposition table, or a dedicated evaluation hash table, one may use a fast hash function to compute an index from the white and black pawn bitboards on the fly, i.e. either a modulo or a multiplication and shift à la magic bitboards by the difference of the disjoint pawn sets ^[2] . To verify correct entries while probing, one needs either to store (a part) of the dedicated Zobrist/BCH key, or for 100% correctness 2*48 bits from the pawn occupancy bitboards. This value could be further compressed with the expense of more calculation overhead by means of n-like men:

$\sum\limits_{wp=0}^{8}\sum\limits_{bp=0}^{8}\frac {48!}{wp! (48-wp)!}\frac {(48-wp)!}{bp! (48-wp-bp)!} = 2^{55.45}$

This can be further reduced by mirroring the board, considering symmetric positions or detecting illegal positions.

Forum Posts

1999

Q: pawn hash? by Scott Gasch, CCC, July 20, 1999
regular hash key & pawn hash key together - good idea? by Tom Kerrigan, CCC, September 16, 1999

2000 ...

A question about pawn hash tables by Andreas Herrmann, CCC, September 13, 2000
A few hashing questions by Severi Salminen, CCC, December 02, 2001
Pawn Hash Collisions in Crafty by David Rasmussen, CCC, December 05, 2001
Crafty's 32-bit pawn hash collision figures? by Severi Salminen, CCC, December 06, 2001
Pawn hash table: need some helps? by Pham Hong Nguyen, CCC, June 23, 2002
Ultra small pawn hash efficiency by Vladimir Medvedev, CCC, November 21, 2002
programmers: pawn hash tables by Joel, CCC, March 08, 2003
pawn hash tables by Joshua Lee, CCC, August 01, 2003
The key of pawn hash tables is based on what exactly? by Uri Blass, CCC, September 06, 2003
Pawn hashing without Zobrist keys by Gerd Isenberg, CCC, September 12, 2003
Pawn Hash Question by Dan Honeycutt, CCC, March 15, 2004
Which pawn positions go into a pawn hash table? by pd42, rgcc, May 26, 2004
pawn hash by Tor Lattimore, CCC, July 03, 2004
Initialization of pawn hash table by Zach Wegner, CCC, September 26, 2004

2005 ...

About pawn hash tables by Uri Blass, CCC, May 10, 2007
An interesting bug in Hamsters by Alessandro Scotti, CCC, August 02, 2007 » Hamsters

2010 ...

Pawn Hash by Harm Geert Muller, CCC, March 18, 2010
Possible pawn hash speed optimization? by John Merlino, CCC, September 19, 2011

2015 ...

pawn hash and ep by J. Wesley Cleveland, CCC, February 01, 2016
Buckets for pawn hash? by J. Wesley Cleveland, CCC, February 04, 2016
pawn hash and eval tuning by J. Wesley Cleveland, CCC, February 21, 2016 » Automated Tuning
hash eval, hash pawn or twice ? by Daniel Anulliero, March 19, 2016 » Evaluation Hash Table
Pawn hash by Karlo Bala Jr., CCC, October 06, 2016
pawn hash by Volker Annuss, CCC, November 18, 2016

External Links

References

^ Chess Woodcuts Graphic Arts Woodcut Art by Elke Rehder
^ Pawn hashing without Zobrist keys by Gerd Isenberg, CCC, September 12, 2003

What links here?

Page	Date Edited
AICE	Nov 29, 2017
Alaric	Mar 4, 2014
Alarm	Jun 7, 2017
Amundsen	Sep 3, 2013
Amyan	Dec 10, 2013
Andreas Herrmann	Nov 7, 2014
Atlas (ESP)	Jan 28, 2018
Automated Tuning	Feb 27, 2018
Bagatur	Sep 10, 2016
Bestia	Jan 5, 2013
BigLion	Sep 28, 2016
Bills Bare Bones Chess	Nov 19, 2015
Bison	Sep 29, 2016
Brainless	Jun 24, 2017
Cheese	Feb 17, 2018
Cheng	Jul 30, 2017
chess22k	Apr 23, 2018
ChessV	Jan 21, 2018
Clarabit	Nov 3, 2011
Coiled	Mar 12, 2017
CookieCat	Nov 15, 2016
Dan Honeycutt	Mar 13, 2014
Daniel Anulliero	Oct 3, 2017
DayDreamer	Aug 22, 2016
Defenchess	Mar 18, 2018
Demolito	Mar 1, 2018
Djinn	Feb 8, 2016
Donna	Aug 17, 2017
Dorky	Oct 10, 2016
Eden	Apr 16, 2017
Elephant	Sep 19, 2016
ESC	Aug 14, 2013
Ethereal	Mar 20, 2018
Evaluation Hash Table	Dec 4, 2016
Exacto	Oct 3, 2015
Flux	Jan 12, 2016
Freyr	Mar 6, 2014
Galjoen	Mar 19, 2018
Gaviota	Jan 21, 2018
GES	Sep 13, 2015
Gibbon	Dec 23, 2014
Gk	Oct 9, 2017
Gogobello	Jul 30, 2017
GopherCheck	Feb 3, 2017
Hagrid	Apr 12, 2016
Hakkapeliitta	Apr 26, 2016
Hamsters	Apr 11, 2014
Harm Geert Muller	Mar 31, 2018
Hash Table	Jan 1, 2018
iCE	Jan 4, 2016
Ikarus	Jul 5, 2016
Incremental Updates	Sep 6, 2017
ISA	Apr 2, 2018
JFresh	Mar 2, 2016
JikChess	Nov 29, 2015
John Merlino	Feb 26, 2015
Joker IT	Sep 16, 2017
KingSlayer	Oct 17, 2016
Kiwi	Sep 2, 2016
LittleThought	Nov 7, 2016
Madeleine	May 18, 2017
Marvin	Feb 10, 2018
Material Hash Table	Apr 3, 2014
MChess	Feb 26, 2018
MessChess	Mar 6, 2014
Monsoon	Feb 8, 2015
Muse	May 17, 2016
NoraGrace	Nov 23, 2014
Nullmover	Jul 21, 2013
Pawn Endgame	Oct 11, 2017
Pawn Hash Table	Feb 1, 2018
Pawn Structure	Oct 2, 2017
Pepito	Nov 27, 2014
Pharaon	Sep 2, 2017
PolarChess	May 15, 2017
PostModernist	Jan 7, 2016
Protector	Oct 12, 2017
RedQueen	Nov 13, 2017
Requiem	Feb 5, 2018
Robocide	May 11, 2016
Rodent	Jan 11, 2018
Rodin	Feb 7, 2016
Schooner	Feb 2, 2018
Scidlet	May 31, 2014
Scorpio	Mar 28, 2018
Scott Gasch	Nov 29, 2016
Searcher	Sep 26, 2016
SEE	Jan 14, 2013
Severi Salminen	May 7, 2015
Shared Hash Table	Sep 11, 2017
Sharper	Jun 6, 2017
Sinobyl	Jul 3, 2014
Sloppy	Sep 17, 2016
Slow Chess	May 17, 2016
Snitch	Apr 7, 2016
Stockfish	Apr 7, 2018
Thor's Hammer	Nov 23, 2013
Tor Lattimore	Jan 13, 2013
TRACE	Feb 14, 2013
Transposition Table	Apr 19, 2018
Uri Blass	Feb 26, 2018
Vajolet	Jan 25, 2018
Vladimir Medvedev	Jul 22, 2016
Wasp	Nov 24, 2017
Wing	Oct 26, 2017
Witz	Nov 14, 2017
Xiphos	Apr 22, 2018
ZChess	Jan 8, 2016
Zurichess	Mar 12, 2018

Up one level

Pawn Islands

GerdIsenberg — Thu, 04 Mar 2010 17:17:23 GMT

Home * Evaluation * Pawn Structure * Pawn Islands

Pawn islands of either side are groups of pawns (at least one), separated by files without own pawns. Those files are therefore either halfopen or open. All other things being equal, the side with fewer pawn islands has an advantage, because the individual pawns are easier to defend against enemy attacks. Each island has a west- or east border file. Rook-files may be the most outer borders.

What links here?

Page	Date Edited
Bismark	Apr 22, 2015
Chexa	Feb 18, 2014
Dispersion and Distortion	Nov 11, 2017
Doubled Pawn	Mar 27, 2017
Gogobello	Jul 30, 2017
Hans Kmoch	Nov 11, 2017
Pawn Islands	Mar 4, 2010
Pawn Islands (Bitboards)	May 4, 2017
Pawn Structure	Oct 2, 2017
Requiem	Feb 5, 2018

Up one Level

Pawn Islands (Bitboards)

GerdIsenberg — Thu, 04 May 2017 09:42:58 GMT

Home * Board Representation * Bitboards * Pawn Pattern and Properties * Pawn Islands

		Pawn islands of either side are groups of pawns (at least one), separated by files without own pawns. Those files are therefor either halfopen or open. All other things being equal, the side with fewer pawn islands has an advantage, because the individual pawns are easier to defend against enemy attacks. Each island has a west- or east border file. Rook-files may be the most outer borders.
Samuel Bak - Drowned ^[1]

Sample Filesets

Black has three islands here, white two:

 . . . . . . . .
 b . . . . . . b
 . b . b b . b .
 . . . . . . . .
 . . . . . . . .
 . w . . . w . .
 w . w . . . w w
 . . . . . . . .

Those are the black and white filesets, one byte each.

 b b . b b . b b
 
 w w w . . w w w

Island Borders

Based on filesets, we can simply determine the west- or east border-files of each island. By shifting left or right one, xor with the original fileset to get all the 0-1 or 1-0 transitions - to finally intersect it with the original fileset to restrict the transitions inside this set of occupied files. The result are the files with half-isolanis.

Since conjunction is distributive over xor, one may alternately swap both operands. In fact it is the relative complement of the shifted files in files and takes three operations each.

East

 b b . b b . b b
 . b . . b . . b
 
 w w w . . w w w
 . . w . . . . w

BYTE islandsEastFiles(BYTE f) {return f & (f ^ (f >> 1));}
BYTE islandsEastFiles(BYTE f) {return f ^ (f & (f >> 1));}
BYTE islandsEastFiles(BYTE f) {return f &     ~(f >> 1) ;}

1 . . . 1 1 . .  files
. . . 1 1 . . .  files >> 1 (board left or west)
1 . . 1 . 1 . .  xor       -> all the west 0-1 or 1-0 file-transitions
1 . . . . 1 . .  and files -> east files of each island

West

 b b . b b . b b
 b . . b . . b .
 
 w w w . . w w w
 w . . . . w . .

BYTE islandsWestFiles(BYTE f) {return f & (f ^ (f << 1));} // ... (f+f)
BYTE islandsWestFiles(BYTE f) {return f ^ (f & (f << 1));}
BYTE islandsWestFiles(BYTE f) {return f &     ~(f << 1) ;}

1 . . . 1 1 . .  files
. 1 . . . 1 1 .  files << 1  (board right or east)
1 1 . . 1 . 1 .  xor       -> all the east 0-1 or 1-0 file-transitions
1 . . . 1 . . .  and files -> west files of each island

Number of Islands

Since each island has exactly one west- and one east border-file, the population count of either border-set might be used to determine the numbers of islands, see dispersion. Of course all byte-wise calculations may be implemented by small, preinitialized lookup tables, indexed by fileset (0..255), containing the number of islands, bitboards of isolated files and whatever else. The maximum number of islands is four.

Isolated Files

The intersection of east- and west border-files are already files with isolated pawns.

1 . . . . 1 . .  east files of each island
1 . . . 1 . . .  west files of each island
1 . . . . . . .  and -> isolated files
. . . . 1 1 . .  xor -> resets isolated files

To isolate wider (2..8) islands is not that hard either.

External Links

Glossary of chess from Wikipedia - P
King Crimson - Islands, 1971, YouTube Video
lineup: Robert Fripp, Boz Burrell, Ian Wallace, Mel Collins, Peter Sinfield with Keith Tippett, Mark Charig, Harry Miller and Robin Miller

References

^ Chess in the Art of Samuel Bak, Center for Holocaust & Genocide Studies, University of Minnesota

What links here?

Page	Date Edited
Dispersion and Distortion	Nov 11, 2017
Duo Trio Quart (Bitboards)	Aug 18, 2017
Hans Kmoch	Nov 11, 2017
Pawn Islands	Mar 4, 2010
Pawn Islands (Bitboards)	May 4, 2017
Pawn Pattern and Properties	Nov 11, 2017

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