Comments/Ratings for a Single Item

Is computer good in Marseillais Chess?

The fact that one of the best chess players of all time (Alekhine) took the trouble to play at least one game of this variant may count for something.

In trying to tentatively estimate the value of the pieces in this variant, I'd guess that the long range pieces may be worth, say, one and a half times what I give them as in standard chess. Thus: P=1; N=3.49; B=5.25; R=8.25; Q=15 and the fighting value of K=4 (though naturally it cannot be traded).

Wow, this rule change makes a big difference to the game of chess!

The sample games were finished in 4, 7, 18, and 13 moves - each move certainly has much more influence on the game play.

I've been trying to think of ways to "add power" to the game "Chess on an Infinite Plane" without adding more or stronger pieces. This might be a good way to do it (but maybe with some limitations).

Is there anyone who would like to try such a game? I'm open to any new and innovative ideas. If you have any favorite pieces, we can try those also (but I'm looking for more than just a mix of new pieces).

The games in play for Chess on an Infinite Plane are going well so far. I'm just interested in a version which might somewhat amplify the game power a little.

A request was made on another thread for games scores and/or analysis of Marseillais. I ran a self-play match with ChessV using about 12 total hours of thinking. Here is the score:

 1. c2c4        b7b6,c8b7
 2. b2b3,c1b2   b7g2,g2h1 
 3. f1g2,g2h1   e7e5,d7d5 
 4. b2e5,d2d4   b8c6,c6e5 
 5. e2e3,d4e5   a8c8,f8b4 
 6. b1d2,a1b1   d5c4,b4d2 
 7. d1d2,b3c4   c7c5,d8d2 
 8. e1d2,d2c3   h7h6,c8d8 
 9. b1b6,b6b7   g8e7,h6h5 
10. b7a7,a7b7   f7f6,f6e5 
11. g1f3,f3e5   e7c6,c6e5 
12. f2f4,f4e5   e8g8,f8f2 
13. b7d7,d7d8   f2f8,f8d8 
14. e5e6,a2a4   d8d6,g8f8 
15. h1f3,h2h3   g7g5,h5h4 
16. f3b7,a4a5   g5g4,g4g3 
17. a5a6,b7g2   d6e6,e6a6 
18. c3d3,d3e4   a6d6,d6d2 
19. e4f5,f5g4   d2g2,g2g1 
20. g4h4,h4g4   g3g2,f8f7 
21. g4f5,f5e4   g1a1,g2g1=q 
22. e4d3,d3c2   a1f1,f1f2 
23. c2d3,d3e4   f7e6,g1g6
black wins by checkmate

Also, there have been 12 games completed on Game Courier. You can find the game logs by following this link.

I expect 23 moves is probably in the neighborhood of what a well-played game of Marseillais should last.  Double moves lead to sharper tactics and bloodier games.  For example, defending a piece doesn't necessarily accomplish much, since the opponent can use his two moves to take the piece and then move the attacker away to a safe location (a kind of hit-and-run.)  Also consider that each move is really two moves, so this game had the equivalent of about 45 moves of conventional chess.

Unfortunately, if you run this test with ChessV it is going to crash.  There's a bug I discovered when trying to run this that I first had to track down and fix.  The version I recently posted was a "release candidate" to get it out into the wild so I could get people doing more testing and reporting problems.  So far about a dozen bugs have been found and fixed.  I hope to release an update shortly - possibly this weekend.  Then you'll be able to run similar tests.  The short explaination is that there was a bad interaction between the double-move and the code that handles en passant.

Why 12 hours?  Somewhat arbitrary.  The longer you let it think, the deeper it can think.  But the time required to reach the next level of depth increased exponentially, and the exponent can be quite high.  To reach enough extra depth to make a difference in skill might require a couple of days.

I should also point out that Marseillais is different enough from standard chess that we don't really know how to best program a computer to play it.  We are in uncharted waters here.  Almost certainly there are changes that need to be made to the standard chess algorithm for proper play of double-move variants, but we do not yet know what those changes are and it will take a lot of study and experimentation to find them.  If you're really interested in the details, chess programs have something called Quiescent Search that is very important, but this concept doesn't really work for double-move variants and it is not clear what should replace it.  You can read about quiescent search here.

But, all that said, this score is of what is probably one of the highest quality games of Marseillais ever played. Humans don't really know how to play it well either. Every aspect of standard Chess has been studied deeply for hundreds of years. But, as you saw for yourself when you went searching out samples games and analysis for double-move variants, there isn't much available. But stay tuned. This is an area that will hopefully see more development in the future. Now that there is a GUI that can run double-move games, hopefully some other chess programmers will make engines that are capable of playing them.

I ran the game giving each side 8 hours on the clock.  Didn't wind up using all the time, though, because the game ended first.  You never really know for sure how much time you should use for any given move because you don't know how long the game will last.

Regarding Chess on a 12 x 12 Board, I've played a few games here.  You can find the logs on Game Courier.  It seems there is definitely a use for "flanking" - going outside and around.  You can get a rook moving on the very first move if you want.

While fixing a bug in the Game Courier code, I came across a situation that is not clearly covered by the rules. Suppose a Pawn makes its usual first-move double move, then it moves forward one more space on the same turn, so that it moves a total of three spaces forward. Can it be captured by en passant if the opponent has a Pawn in the usual position? On the one hand, it has made a double move, and a Pawn that makes a double move can normally be captured by en passant. On the other hand, it is no longer on the space it moved to when making its double move, and if the player had wanted to, he could have moved the Pawn forward one space, then captured the Pawn that was in a position to capture it by en passant if it had made a double move.

For now, I have written the code to forbid en passant capture in this situation. Does anyone know if there is any precedent for allowing en passant capture in this situation?

This is tricky, and different players have used different rules.  This page states:

According to Pritchard's Popular Chess Variants, 'The en passant rule has seen change. Modern players allow it only when the Pawn advance formed the second move of a turn.'. This helps to eliminate some ambiguity discussed in the comments. (What if a player advanced a Pawn by two squares, then occupied the intermediate square with a piece?)

The situation is potentially even worse than this example.  What if a pawn made a double move and then went on to capture a piece with its second move?  Would capturing it en passant then magically bring back the piece it captured?

There was a discussion about this on the talk chess site a few years ago.  The discussion went on for quite a while and a lot of people weighed in.  I can try to dig up the thread, but the final outcome was that there is really only one interpretation of en passant makes sense and doesn't lead to problems: the en passant capture must be made with a player's first move and can only be used to capture a two-space move by the opponent's second move.  If a player makes a two-space pawn move with the first of his two moves, it is not subject to en passant.  ChessV uses this interpretation and I believe Game Courier should do the same.

In any case it should be clear that you can never capture a piece after it moved away with the second move, just because it was in a location after its first move where you could capture it. It would be highly illogical if e.p. capture would be an exception to that. Whether you want a second move done with a different piece to destroy e.p. rights is a matter of choice.

I changed it to allow en passant only when the Pawn's double move is a player's second move, and I confirmed that this change did not break any past game. But as I was rewriting the rules, one more thing occurred to me. Suppose a Pawn's double move done on the first move puts a King in check, thereby ending the turn without a second move. If this check could not be ended with an en passant capture, this could allow a King to be checkmated in a position that would not be checkmate in Chess, and this would violate the intention behind the game.

So, I think we have to exclude the rule that en passant is allowed only when a Pawn makes a double move on the second move of the turn. This could be replaced with the rule that en passant is allowed only when the double move was the opponent's last move, or it could be replaced with the rule that en passant is allowed only when the Pawn that made a double move didn't make another move after it. For the meantime, I'll change it back to the latter.

Well, another move should clear the e.p. rights generated by any previous move. Like it always does. E.p. rights are transient, and last only to the end of the next move. (And not to the end of the next turn!)

Yes, I should have said en passant only allowed if the two-space pawn move was on the player's most recent move (rather than second move) to account for this.  I just tested this situation and ChessV does allow en passant to get the king out of check.  It is implemented as H. G. suggests - any move clears the EP square.

The earliest source I can find is Pritchard's 1997 Encyclopedia, which is the source Hans originally used to write this page. It says "En passant is legal if the opponent moved a pawn two squares on either of his moves but the capture must be made at once. However, if the opponent made two two-square pawn moves, both pawns can be taken e.p. This last rule is credited to Alekhine by F. Palatz in an article on the subject (LEC Sep 1928)." LEC refers to L'Echiquier. Notably, Alekhine is not one of the inventors, and how the game should handle en passant might be something that the original inventors didn't think of. It is also unknown whether the game was invented by Fortis or by de Queylar. It has been attributed to each one, but its origins are murky.

Regarding one of the alternative rules, it says "The game was sometimes played with alternative rules: a check on the first move was illegal and a player could not capture e.p. if the pawn had been moved in the first part of the player's turn." It's very possible that Fortis and de Queylar invented similar games with slightly different rules that eventually got conflated together.

The rule that Greg Strong and H. G. Muller propose has the advantage of being the simplest to program. It works with code that has already been written for Chess. Of course, the original inventor of the game would not have had this in mind, since programming games was not an option when it was invented. However, the rules as initially described above can be programmed, and that's what I have done in Game Courier. The only issue with them is that they need emendation for a Pawn that moves twice on the same turn. If we keep those rules, then en passant capture should be impossible in this instance, or it should be allowed for the Pawn on its new space. I have the former programmed right now, whereas the latter would be trickier to program.

So if the player moved a pawn two spaces and the placed a piece on the square passed over you would allow capture of both with a single move?  To me, that doesn't fit comfortably with the spirit of chess.  Pritchard notes that the rule has changed over time, probably for good reason.  Similarly, Marseillais Chess is now played in 'balanced' form because it is clearly superior.  Old games do evolve and that's a good thing.

Here is the thread on Talk Chess where this was discussed.  In it I actually started iwth Fergus' view and was persuaded to adopt my current view.

What I cannot imagine is that the original inventor would have thought it reasonable to allow e.p. capture

1. when the capturing Pawn has not seen the other one move past it
2. when the Pawn that moved is no longer there
3. when the e.p. square gets occupied

So if the player moved a pawn two spaces and the placed a piece on the square passed over you would allow capture of both with a single move? 

The way it is coded, that would not happen. The first thing it checks for is an ordinary diagonal capture. If the move involves one, that's what it does, and it doesn't get around to checking for an en passant move.

I have started to look at the thread you provided a link to, and I will continue to look at it tomorrow.

What I cannot imagine is that the original inventor would have thought it reasonable to allow e.p. capture

1. when the capturing Pawn has not seen the other one move past it
2. when the Pawn that moved is no longer there
3. when the e.p. square gets occupied

That's all reasonable, and what I've coded for Game Courier is in conformity with it. The first one is already handled by the rule that en passant is not allowed on the second move unless the player is making two en passant captures. This prevents a player from using his first move to move a Pawn into position to do an en passant capture. (Note that a Pawn that was already in the position to do this could just capture the double-moved Pawn normally and then use its second move to go to the space the now captured Pawn had passed over, reaching the same position without using en passant.)

The second is handled by setting the ep1 variable to false whenever a player moves the same Pawn again. Since ep1 would store the position of the previously moved Pawn if the last move were a Pawn move, it checks whether the second move is from that location.

The third is handled by checking for a normal capture before checking for other types of Pawn moves. If the move is a normal capture, it never gets to the code for en passant. If it's not a normal Pawn capture, then the move was to an empty space. By the time it reaches the elseif clause for en passant, it has already been determined that the space is empty.

One more issue has come up. Suppose that a player makes a first move that leaves him with no legal second move. Does this end his turn like a checking move would, or does it end the game in a draw? Pritchard says in Popular Chess Variants, "A player who is not in check and cannot complete his turn is stalemated." This suggests the latter, but he could have said it more explicitly if that is what he meant. Is there any consensus on how being unable to move on the second move should be handled?

Tough Question.  I could see the 2nd move being "pass", and if Marseillas is a mandatory 2 move game per person, it is a strong arguement that it is a stalemate.  You are the programmer to the game, I would pick the one Fergus Likes, and make sure it is mentioned in the rules.

It seems logical to me that stalemate must be a result of one player's move making it impossible for the other player to complete his move(s). Intentionally "stalemating" yourself on your first move so you have no legal second move seems like it should be illegal - an illegal move. If left with any set of 2 legal moves to be played, a player should be compelled to make those moves.

If, for example, a player can only move his pawn, that pawn starts on b7, and an enemy pawn is on b4, that player should not be allowed to make the pawn double-move on move 1, but rather make 2 separate single-square moves.