BBO Discussion Forums: Bug in Gib opening leads - BBO Discussion Forums

South does not have their bid.Was Geo day 2 mp

Opening lead was 3♣,

Try and convince me that any lead other than the Q♠ partner' suit isn't a bug.
Gib has stopped leading partner's overcall suit. The older commercial Gib program will lead partner's suit. The logical conclusion is that the programmer's have introduced a bug which prevents Gib from leading partner's suit.

Everyone knows you can easily find more examples of this.

I think it's insane to think that they are deliberately preventing leading partners suit, or would put in something that would lead to this. GIB leads partner's suit -- sometimes. It doesn't have human biases of gravitating heavily towards leading partner's suit in unclear situations; humans strongly lean towards this when it's unclear because it's defensible in the post-mortem; partner can hardly criticize you when it doesn't work out. When the club lead happens to be better he won't say anything. So we tend to lead partner's suit even when we suspect another lead is better, unless it's overwhelming in our estimation that the other lead is better.

GIB tries to construct a sample of hands that match the auction and leads what works best statistically. FWIW my copy of standalone GIB also leads a club, and it indicates that it thinks the margin between club & spade is pretty miniscule. But this is based on south presumed to have long strong diamonds; if south has distorted massively obviously this will throw off west's conclusions. It's unusual to be holding diamond K and south really having their bid, so maybe we disagree with the hypothetical hands it will generate for South, that are close to but not necessarily matching the book definition.

Any bug would be errors in generating representative hands in the bidding, it is hard to cater to total psyche by opponents. But I think you have to overcome your human bias of rage when partner doesn't always lead your suit. I am sure that humans blindly lead partner's suit more often than truly optimal.

 Stephen Tu, on 2018-June-25, 10:47, said:

I agree that is the answer why GIB often doesn't lead partner's suit when it should, and also the problem.

Look at a couple of main cases. Partner has opened the bidding in a suit, or overcalled in a suit. If partner opened 1♠, there is no guarantee of suit quality, just suit length. If partner overcalls 1♠, a human player would assume a generally better suit than for a 1♠ opener. This is especially true for 2+ level overcalls. I don't know that GIB makes any distinction.

 johnu, on 2018-June-25, 11:56, said:

Just happened. I had overcalled 1S and they reach 3NT. GUBBO did not support spades and opening lead was s8 from Q86. Just a vulnerable game.

 johnu, on 2018-June-25, 11:56, said:

OTOH, partner did not open 2s, so he likely has 5 spades only. So would need exceptionally good spades + intermediates, + an entry, for spade lead to be overtaken and continued for it to be effective. Also you are the one with diamond entry, not partner, and won't have spade to continue. GIB might well be right that it's easier for partner to come up with some decent club cards.

 Stephen Tu, on 2018-June-25, 12:25, said:

Of course, you could be right and obviously any lead could be right. But see post #4 (although complete hand wasn't posted). The point I was trying to make is GIB shouldn't assume 1♠ overcall is on a random 5 card suit.

 johnu, on 2018-June-25, 13:55, said:

It doesn't assume a random 5 card suit. It assumes a suit that GIB itself would overcall on. So I would say the opposite; I see humans overcalling with much worse suits than GIB does.

Steve, if you want to say the club lead is a bug, you're going to have to actually provide some backup to your assertion, rather than just 'it should lead a spade because that's what everyone does'. Try some simulations of what you think East should have for a spade overcall and post your results.

I'm struggling to think of any hands where a spade would work much better than a club given South's near-solid diamonds. So Stephen Tu is probably right; I expect South psyched / didn't understand what 3nt means and you're asking for GIB to assume he is playing with beginners and act accordingly.

 smerriman, on 2018-June-25, 14:38, said:

Every person out there knows personally of 20+ examples where Gib hasn't led there suit or has declared hand where Gib hasn't led a suit bid and not leading the suit bid was a clear error.
Go to previous posts on the subject, it is a clear problem.
My example may not be the best, but is -3 on a spade lead.

 smerriman, on 2018-June-25, 14:38, said:

Gib doesn't overcall on crap. There is every reason to believe Gib has a decent suit and out-side entry.

Opening leader has only 4-card suits. Seems obvious to me lead partner's suit and knock out the one stopper declarer has. There is no reason to think leading our ratty 4-card suit will be better. If partner has a second good suit they can lead it when they get in. (This situation where partner finds the killing switch is supposed to be part of Gib's leading methods)

can be beat on other leads, but defenders never lead spades and ended up in a situation where they were squeezed and didnt keep the right cards.
Gib just refused to lead QS at several opportunities. Leading QS at any of it's opportunities would have made situation clear enough would have likely beat 3N but not -3, that happens only after an initial spade lead.

 Stephen Tu, on 2018-June-25, 12:25, said:

Other than the hand I just mentioned and other similar hands where it led the middle card GUBBO has mostly led well. Especially in cases where it manages to find your stiff on opening lead to give you a ruff.

The other bad case is where it does not lead back your suit at 3 NT. I believe this has been looked into and is in the list of potential bug fixes.

 steve2005, on 2018-June-25, 15:57, said:

So what? You are drawing conclusions based on selective subset of hands that frustrate you. You've probably forgotten many hands where it didn't lead your suit and it worked out fine, or better than leading your suit. A more valid way of looking at this, rather than cherry-picking hands that didn't work out, is to go into your hand history, and look at say the last 100 hands where partner was on lead, you had overcalled, and it stubbornly led something else. Then tally up how many times this was double dummy worse, vs better, vs even. Then we can have more productive discussion.
I'm pretty sure that if they hard coded GIB to auto lead partner's overcalled suit, that overall performance would drop considerably. The methodology for picking opening leads is theoretically sound. The only issue to me is particular auctions; some they may not be generating truly representative sample hands for the opponents. Like if they have reached 6nt off 2 aces or the like, the bot should be simulating hands with very long running suits, and cash out, rather than thinking the aces can't go away and hunting for the extra undertricks by being passive.

On this hand, I don't know about you, but at favorable vul with moderate values and some shape I am sticking in 1s on all kinds of hands, I'm not waiting to hold 4 of the top 6. I'm catering to partner having a fit and raising, successfully competing to 2s/3s, and hoping for spade lead if fit (not necessarily with only stiff, vs NT), and if not I hope it's hard for N/S to know to x me at 1 level instead of aiming for 3nt at unfavorable. If I'm on lead vs someone who overcalls like I do, I expect declarer to have double stop way more often than not, and sometimes triple stop. I personally don't believe in lead direction as priority 1 for overcalling, for me it's way down on the list vs. competing for the partial and nuisance obstruction. Yes it means partner will sometimes lead the wrong thing vs me being silent, but over the years I've won a lot more than I've lost waiting for better suits.

I found the actual hand:


Obviously 3NT is insane.

Challenge: come up with a single example where South's bid is not insane (at least a spade stopper and a reasonable chance of 3NT), and it's important to lead a spade and not a club to beat the contract.

A hand from the 2nd set of the final of the BBO forum event. Any idea why the advanced GIB did not cash ♥A? (cause your side bid the suit)<br style="background-color: transparent; color: rgb(28, 40, 55); font-family: arial,verdana,tahoma,sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 20px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; orphans: 2; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;"><br style="background-color: transparent; color: rgb(28, 40, 55); font-family: arial,verdana,tahoma,sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 20px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; orphans: 2; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;">
https://bit.ly/2w5WJZw

advanced robots challenge match<br style="background-color: transparent; color: rgb(28, 40, 55); font-family: arial,verdana,tahoma,sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 20px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; orphans: 2; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;">another bad lead: trump the only lead which hurts. here K♠ or ♦ should be safe.<br style="background-color: transparent; color: rgb(28, 40, 55); font-family: arial,verdana,tahoma,sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 20px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; orphans: 2; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;">obvious south has 1♥ so need ten or Q to be ok.<br style="background-color: transparent; color: rgb(28, 40, 55); font-family: arial,verdana,tahoma,sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 20px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; orphans: 2; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;"><br style="background-color: transparent; color: rgb(28, 40, 55); font-family: arial,verdana,tahoma,sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 20px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; orphans: 2; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;">South should double diamonds but still safer to lead ♦<br style="background-color: transparent; color: rgb(28, 40, 55); font-family: arial,verdana,tahoma,sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 20px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; orphans: 2; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;">sure diamonds is a minor. choice has to between diamond and spade<br style="background-color: transparent; color: rgb(28, 40, 55); font-family: arial,verdana,tahoma,sans-serif; font-size: 13px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; line-height: 20px; margin-bottom: 0px; margin-left: 0px; margin-right: 0px; margin-top: 0px; orphans: 2; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;">hand


2 for now

2S here makes no difference. but surely TH is best lead.

Your post is broken, but my challenge was regarding the hand you posted. If you think the club lead is so bad compared with the queen of spades, demonstrate a layout that requires the queen of spades lead and doesn't require a 100% psych. Should be easy if the lead is that bad.

 steve2005, on 2018-June-25, 20:55, said:

"Surely" seems to me to be a massive overbid. South's hand is unusual; usually you expect short hearts in south not North. Why can't partner have some AJxxx type heart overcall, and heart lead sets up pitches in South, while partner has diamond honors behind declarer? Or maybe partner has say DKx behind declarer, by leading diamonds may set up diamond ruff your side. In any case it seems unlikely that short hearts in south are going to go away on diamonds; with your spade control you'll have another chance to lead through declarer's Hx of hearts if he has it. So to me it doesn't seem "sure" at all. It's likely a lot closer than you think. And if heart lead low is better than T, South may have like Kx and North Q9x, it's hard to construct hand where T is superior.

I think you have a hang-up about this and just massively overrate leading partner's suit, think the odds massively favor it more than actual reality. Maybe you have had human partners who have berated you for not leading their suit when that would have worked, and that got you into this mindset of *lead partner's opened/overcalled suit in anything less than 100% clearcut cases, anything else is ridiculous*. But reality may not match up to your bias. Like I said, instead of cherry picking, you have to look at *ALL* hands over some extended set (say at least 50?) where GIB didn't lead the overcall suit, and carefully record statistics about whether this gain/cost/no difference. Otherwise the ones where it didn't work out are going to automatically stand out in your mind.

BTW in your original hand that prompted this post, it's like 1000x times more obvious for East to keep a diamond in the end game (South is not playing this way with KJ of diamonds) than for West to lead spade over club on opening lead.