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Subject: Bug in computer version? rss

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Was George Orwell an Optimist?
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I've begun learning Arimaa, and downloaded a freeware computer game to get a feel for how it works. The about box shows the following:

Arimaa Version 2.0
Copyright (C) 2005 by David Fotland


I was making good progress, having captured a horse, but somehow triggered a bug and am wondering if anyone has experience with the program and can offer suggestions.

All seemed to be well after I moved my third step:



I had begun the move with my dog in the C3 trap, protected by my elephant in D3. My first three moves were dog to C4, dog to D4, elephant to E4, trapping the gold elephant.

My fourth move was rabbit from B8 to B7, after which I got this:



A whole series of error boxes follow, and once they are finished gold does not move. My first thought was that the bug happens because I've hemmed in the gold elephant, but I've tried undoing the rabbit move and moving the elephant back to D4, with no better results. I've tried pretty much all the available moves for my fourth step, and they all lead to a similar series of error popups.

Is the game simply too buggy to use, or does anybody know of a patch that corrects this? There is a link to purchase an upgraded version with stronger AI, but I won't consider that without knowing that it also corrects the known bugs.

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Billy McBoatface
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Have you contacted David Fotland directly? I have met him and he's a very nice guy. Most likely he'll be able to tell you whether or not this is a known bug (and whether or not it is fixed in the pay version of the software).
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I don't have an email address for him. Maybe I can find contact info at the website where they sell upgrades...
 
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Fritz Juhnke
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Sphere wrote:
Is the game simply too buggy to use, or does anybody know of a patch that corrects this? There is a link to purchase an upgraded version with stronger AI, but I won't consider that without knowing that it also corrects the known bugs.

I have never encountered the bug you describe, either with the free version (only a few games) or the full version (dozens of games). I have encountered the "Illegal Move" popup many times, but usually because I am not dragging precisely enough, so the interface thinks I mean a different destination square. Also, of course, I get the "Illegal Move" popup when I try to make an illegal step. But I have never seen it give the "Illegal Move" popup when I was trying to make a legal step with accurate click and drag.

I will set up your exact position tonight to see whether my copy of Bomb will give me an error in the same circumstance.
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Billy McBoatface
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Geekmail, containing email address, sent.
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Fritzlein wrote:
I will set up your exact position tonight to see whether my copy of Bomb will give me an error in the same circumstance.


Thanks.

wmshub wrote:
Geekmail, containing email address, sent.


And thanks to you - email sent.
 
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Fritzlein wrote:
I have never encountered the bug you describe, either with the free version (only a few games) or the full version (dozens of games). I have encountered the "Illegal Move" popup many times, but usually because I am not dragging precisely enough, so the interface thinks I mean a different destination square.


In that case, I assume you get only the one popup. I got a series of 6 or 8, one following the next, as the AI apparently considered illegal moves.

I wish now that I'd done more screen shots, to collect the full sequence of error messages. As a software engineer, I know that would be the most helpful course to somebody debugging the code, but I got interested in playing around with various levels of "undo" to see if I could isolate the triggering condition.
 
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Fritz Juhnke
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Fritzlein wrote:
I will set up your exact position tonight to see whether my copy of Bomb will give me an error in the same circumstance.

Aw heck, I just set it up here at work. Hopefully nobody saw me. Anyway, Bomb not only allowed me to play the move it refused to let you play, it cheerfully suggested mf4n Ef3n Ef4w mf5s in response, with an evaluation of -3.13 at eleven steps depth.

Of course, the behavior could be different in analysis mode than when actually playing, but at least we know the problem isn't in Bomb's understanding of legal/illegal moves.
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Fritz Juhnke
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Sphere wrote:
In that case, I assume you get only the one popup.

Yes, only the one popup, and whenever I got it the offending piece jumped back to its original square. I see now from your screenshot that your rabbit stayed where you moved it. So I guess the implication is as you stated, namely that the program is not complaining about your move, since it let you play it, but rather complaining about its own illegal move. I have never seen that.

When in analysis mode, the output will log quiescence search errors, which consist either of Bomb failing to statically detect a goal that search later finds, or of Bomb trying to generate a search extension via an illegal move. But those errors always seem to be caught, handled, and logged.

And also there are occasional errors of analysis, where Bomb might insist that there is a forced goal in three when actually a defense exists. But that isn't the type of bug you are talking about, and anyway Bomb plays quite a strong game in spite of its search/evaluation glitches.

By the way, I trust that when you were undoing steps, you used the "Undo" button (black triangle with a red X) rather than the "Back" button (black triangle only). The Back button is useless, because it affects only the display, not the state of mind of the engine, whereas the Undo button is extremely useful to revert to a prior state of the game. I can only recall once when the AI got stuck and unable to make a move, and that was when I had used the Back button. But that was probably a different circumstance, because I didn't get the series of popup errors.

I have been extremely happy with the software overall, but the value of a purchase for you probably depends on whether Fotland returns to active Arimaa development. The purchase price includes all future upgrades, so I got a free upgrade from the 2004 engine to the 2005 engine. But there have been no updates since, because Fotland was distracted by Go (His program Many Faces of Go reclaimed the World Championhip), and because Bomb remained Arimaa World Champion year after year even without improvements. Hopefully Bomb's defeat in 2009 will inspire Fotland to turn his attention back to improving Bomb, but that is far from guaranteed.
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Fritzlein wrote:
So I guess the implication is as you stated, namely that the program is not complaining about your move, since it let you play it, but rather complaining about its own illegal move.


That's right. I've already received a response from David, and he says the multiple popups suggest that I may have found a bug in the AI.

There's not enough info for him to pursue it, though - I need to save the game and send it to him for that. I hadn't even realized there was a save game feature yet, although that seems obvious in retrospect.

I've just tried several times to go down the same road, but am not having any luck reaching the position. Seems like I've got a challenge to pursue!

Fritzlein wrote:
When in analysis mode...


Hadn't seen that, either. Was basically just test-driving to see if I understood the rules, and got into an odd corner.

Fritzlein wrote:
By the way, I trust that when you were undoing steps, you used the "Undo" button (black triangle with a red X) rather than the "Back" button (black triangle only).


That's about the only thing I did have right.
 
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Fritzlein wrote:
I see now from your screenshot that your rabbit stayed where you moved it. So I guess the implication is as you stated, namely that the program is not complaining about your move, since it let you play it, but rather complaining about its own illegal move.


I think that's more than implied - note the "Gold to move" prompt. I'm also guessing that the "Search called not at phase 0!" isn't something you normally see; it's probably related to an unexpected state of the AI as it searches the problem space.
 
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I wonder if the computer ran into trouble with the superko rule. Some go programs ignore superko when computing their moves; I know this because I sometimes get bug reports when these programs get errors on my go server (which implements superko correctly).

If the move generator decided that a certain move was the best, but the game play logic spotted that this was an illegal move due to superko, then reproducing the error would be difficult; it would require not just setting up the same position, but also getting there by the same sequence.

Sphere, had you been making moves back and forth (ie, on one move undo the previous) just before this happened?
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I've had a similar problem before. I assumed it was because I was running the free version and you can only play a limited number of turn, perhaps it wasn't, its been ages since I played it though (cool game).
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Sphere wrote:
I'm also guessing that the "Search called not at phase 0!" isn't something you normally see;

Oh, actually I often do see that error when I am analyzing. It happens in two circumstances. (1) I sometimes enter a three-step move and forget to pass the fourth step before asking Bomb to analyze the resulting position, or (2) I sometimes undo the wrong number of steps when backing up, and thus ask for an analysis starting in the middle of move.

That makes me wonder what the Undo button does to the playing mode. When I am analyzing, I make the moves for both sides and the engine does nothing until I ask it to. This is in contrast to play mode where it automatically starts thinking for the other side whenever I make a move for one side.

But what happens when I try to undo moves in the middle of a game being played? The engine can't automatically start thinking when it gets to the beginning step of one of its moves, because that would prevent me from undoing multiple moves before resuming. We would be fighting for whether it would get to make another move or I would get to undo further back. So it must instead somehow go passive until you kickstart it again.
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wmshub wrote:
Sphere, had you been making moves back and forth (ie, on one move undo the previous) just before this happened?


I'm honestly not sure. I was just cruising along thinking about the situation when things blew up. Then I got involved trying to figure out why, rather than documenting the position first. I really wish I had just saved immediately after it happened.
 
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