smerriman

But there's no symmetry; you would never double with 5 spades and 4 clubs, but would the other way around. So partner will be giving preference to the minor when having 3-3, meaning you'll miss spade fits. And yes, it has two suited options (both 2nt and 2♦ iirc.)

The first double with 5 spades seems just as bad to me.. It doesn't really matter what basic GIB does here, because it's clearly something advanced GIB should decide. Can anyone definitely say that if you have a proper hand for both doubles, passing is worse? I looked at some of GIBs sims and the times when 4♥x was making, 4♠x was going down more.. [edit]sorry, this was incorrect, it was more that 4♥ was going down most of the time.

Your bidding diagram has the wrong opener, which was a little confusing. Otherwise, agreed with the above. While 2NT normally shows two 4 card suits, there's no harm in bidding in here too to catch partner with a 5 card minor.

paulg made a video on the constraints here: If you want E/W to always pass, make sure you leave those seats empty (rather than placing robots in them).

The OP was playing against 2012 robots...

That makes its play make even more sense, given now we're talking about MPs and while GIB may make the same bid with both, the other hand is at least as likely.

It is extremely well-known and has been stated many times over (by myself included) that GIB works by performing a very basic algorithm: 1) Generate a bunch of deals roughly consistent with the auction. 2) Calculate the double dummy result for each card you can play. 3) Pick the card that averages the best score. (On top of this, when advanced GIB is declaring, there is a single-dummy algorithm that kicks in after trick 2 that tries to make a plan to avoid putting off guesses. But this is not relevant to defending, or the cases discussed in this post). There is course a lot of complexity in step 1 - how does it find hands that match the auction? What if the auction is impossible, or so rare it can't be simulated? If it allows for some variation - as has been stated by barmar in the past - how does it know if a deal is 'close' to matching? But steps 2 and 3 are trivial. 5 years ago gwnn posted a hand where GIB plays a card at trick 10 that is guaranteed to be strictly worse than any other card, if any nonzero number of hands is simulated: [hv=http://www.bridgebase.com/tools/handviewer.html?sn=gwnn&s=SAT4HK964DAKC9872&wn=Roboter&w=S983HAJT75DJ4CKT5&nn=Roboter&n=SKQJ65HQ82DQ852CA&en=Roboter&e=S72H3DT9763CQJ643&d=s&v=b&b=7&a=1N(notrump%20opener.%20Could%20have%205M.%20--%202-5%20%21C)P2H!(Jacoby%20transfer%20--%205+%20%21S)P2S(Transfer%20completed%20to%20S%20--%202-5%20%21C%3B%202-5%20%21)P3D(New%20suit%20--%204+%20%21D%3B%205+%20%21S%3B%2010+%20total%20points)P3S(Support%203rd%20S.%20No%204th%20D%20--%202-5%20%21C%3B%202-3%20%21)P4C(Cue%20bid%20--%204+%20%21D%3B%205+%20%21S%3B%20%21CA%3B%2013+%20total%20points)P4S(2-5%20%21C%3B%202-3%20%21D%3B%202-5%20%21H%3B%203%20%21S%3B%2017%20HCP%3B%2018)P4N(Blackwood%20%5BS%5D%20--%204+%20%21D%3B%205+%20%21S%3B%20%21CA%3B%2015+%20total%20points)P5H(Two%20or%20five%20key%20cards%3B%20no%20queen%20--%202-5%20%21)D(6+%20HCP%3B%20rebiddable%20%21H%3B%20%21HKQ%3B%2020-%20total%20points)6S(4+%20%21D%3B%205+%20%21S%3B%20%21CA%3B%2015+%20total%20points)PPP&p=S3S5S2S4CAC3C2C5D2D3DAD4DKDJD5D7C7CTS6C6D8D9SAH5STS8SKS7SQC4C8S9DQDTC9H7H2H3HKHJH4HTHQD6H8CJH6HACKSJCQH9]400|300[/hv] That blew the usual 'maybe you just got a very very unlucky set of sims' excuse out the window. It has been bugging me every since - to be honest, it's very rare a week has gone past over the last several years where I don't think "gah, I wish I knew what GIB was doing". While my attempts to get access to the source code have failed, I can finally announce I know why it made (and continues to make) these mistakes. And that is because, rather shockingly, GIB does not perform step 2 as everyone believes it does. -- A couple of weeks ago, Lorand Dali posted about his new AI bridge project. Very interesting stuff and worth a read. I was slightly disappointed to find out it was entirely reliant on a having a pre-existing robot - learning to bid from a huge sample of hands generated by the GIB robot. Until I discovered how he generated the hands - not via online GIB hand records as I had expected, but by piping them into the bridge.exe program that freely comes with the Windows downloadable version of BBO. Wait, there's a free command line version of GIB? Yes - though of course, it's a version from 2012, so extremely out of date in terms of the bidding. If you think GIB has bidding flaws now, BBO did an amazing job of improving it from where it started while they were still working on it. How does this help? Because Matt Ginsberg added some debugging flags, documented in an archived version of his website. While the BBO version appears to have been altered somewhat, with some of the flags not working and some workarounds needed, there's still one available which outputs a trace of all of the simulated hands, how GIB scored them, and how that averaged out to its choice of play. For example, when trying to decide what to lead to trick 1 in gwnn's example hand, it generates 100 hands (this was another flag, I used 100 but BBO will be even less) and displays them each in this format: deal 76: S A Q 7 5 4 H 9 D A K 7 2 C J 7 6 S 9 8 3 S J T H A J T 7 5 H K 6 4 3 2 D J 4 D Q T 6 5 C K T 5 C Q 4 S K 6 2 H Q 8 D 9 8 3 C A 9 8 3 2 West to lead; S trumps mismatch 32.00 CK: 100 CT: 100 C5: 200 DJ: 300 D4: 300 HA: 200 HJ: 200 H7: 200 H5: 200 S9: 200 S3: 200 The first bunch of deals don't include the 'mismatch' line - the last group has increasing mismatch scores, which is presumably widening the range of hands it considers acceptable in include in the the simulation. And then at the end, a conclusion that averaged out of the double dummy results over all of the deals: S3: -24.70 -> 2.45 DJ: -27.70 -> 2.34 S9: -24.70 -> 2.15 D4: -26.70 -> 2.07 HA: -119.20 -> 0.95 HJ: -270.80 -> -0.83 C5: -275.70 -> -0.99 H5: -289.10 -> -1.10 H7: -289.10 -> -1.10 CT: -280.70 -> -1.45 CK: -339.70 -> -2.39 I play S3 I expect the DJ got a slight boost due to signalling, but so far it's all making sense. There's just one small catch. Some of the earlier deals in the set have question marks after some of the double dummy results: deal 0: S A Q T 7 2 H 4 2 D Q 9 3 C 9 7 2 S 9 8 3 S 5 H A J T 7 5 H 9 6 3 D J 4 D K T 8 7 6 2 C K T 5 C A J 6 S K J 6 4 H K Q 8 D A 5 C Q 8 4 3 West to lead; S trumps CK: 300? CT: 400? C5: 400? DJ: 400? D4: 400? HA: 300? HJ: 400? H7: 400? H5: 400? S9: 400? S3: 400? In this case, the first 32 deals have ? after all results, and the remaining 68 have none - though on other occasions, some deals have ? for some play cards and not for other played cards. And most importantly - some of the scores with ? are incorrect. Look at what happens when we get to the crucial card at trick 10 in gwnn's case. The first simulated deal: deal 0: S J H Q 8 D --- C --- S --- S --- H A J T H 4 D --- D 6 C K C Q S --- H 9 6 D --- C J West to play to H2, H3, HK; S trumps N/S have taken 9 tricks HA: -1430? HJ: 100? The question-marked figures say that playing the heart Ace will allow the slam to make - and the J will cause it to go down! In fact, the first 44 simulated hands all have the same conclusion. On deal #44 (0-indexed!), it gets it right for the first time: deal 44: S J H Q 8 D --- C --- S --- S --- H A J T H 9 D --- D 6 C K C Q S --- H 6 4 D --- C J West to play to H2, H3, HK; S trumps N/S have taken 9 tricks mismatch 16.00 HA: 100 HJ: -1430 Note that there is nothing special about this deal that separates it from the others - the exact same hand with East left with holding 9-6-Q appeared several times in the first 44. On deal 45 it's also correct, but 8 of the next 19 hands it has the incorrect figures, before all others are correct. So as the final result, on 52 of the 100 hands, it believes ducking is required to beat the contract - when it isn't true once. When it combines 52*100 and 48*-1430, you get 63440 - which it provides as its final output: HJ: -634.40 -> 0.68 HA: -695.60 -> -0.68 I play HJ Oops. I took a second example, posted by bixby a few months ago, where throws away its high card on trick 10 in a no-win, rarely-tie, mostly-lose scenario. [hv=https://www.bridgebase.com/tools/handviewer.html?lin=st||pn|bixby,~Mwest,~Mnorth,~Meast|md|2SAQ62H53DQTCAJT92,SJ854HDKJ7654C764,SKT9HAQ76DA832C53,S73HKJT9842D9CKQ8|sv|b|rh||ah|Board%204|mb|P|mb|1D|an|Minor%20suit%20opening%20--%203+%20!D;%2011-21%20HCP;%2012-22%20total%20points|mb|2H|an|Aggressive%20weak%20jump%20overcall%20--%206+%20!H;%204-10%20HCP|mb|D|an|Negative%20double%20--%204+%20!S;%207+%20HCP;%208+%20total%20points|mb|P|mb|2N|an|4+%20!D;%203-%20!S;%2011-14%20HCP;%2012+%20total%20points;%20stop%20in%20!H|mb|P|mb|3N|an|5-%20!H;%204-5%20!S;%2014-21%20HCP|mb|P|mb|P|mb|P|pc|S7|pc|S2|pc|SJ|pc|SK|pc|C5|pc|CQ|pc|CA|pc|C7|pc|CJ|pc|C6|pc|C3|pc|CK|pc|H4|pc|H3|pc|D7|pc|H6|pc|ST|pc|S3|pc|S6|pc|S8|pc|DA|pc|D9|pc|DT|pc|D4|pc|S9|pc|H2|pc|SQ|pc|S5|pc|SA|pc|S4|pc|H7|pc|C8|pc|CT|pc|C4|pc|D2|pc|HJ|pc|C9|pc|D6|pc|D3|pc|HK|mc|12|]400|300[/hv] Is this because it was unlucky and every hand it simulated resulted in the equals case? On my run, it found the equals case just 5 times - no question marks: HK: -690 HT: -690 On 19 occasions, it had a definitive value for the heart T, but thought - with a question mark - that throwing the king would get a *better* score HK: -630? HT: -660 On the other 76, it came up with the right values: HK: -690 HT: -660 In this case, that was enough to weight it to making the correct play (it chooses 8 among equals after the analysis): HT: -661.50 -> 0.57 HK: -678.60 -> -0.57 I play H8 But given it's capable of including completely wrong dummy double analysis scores in its calculations, it's no longer surprising with a smaller / different set of hands that the incorrect ones could end up biasing the results enough to play the wrong card. -- Note that it's quite possible that BBO have improved the play engine of GIB since v21, which is the one tested here, though all reports have been that they haven't touched it other than forcing it to lead an ace against 7NT. Conclusion: I don't know why GIB's "double dummy" analysis causes it to give correct scores for some cards, and incorrect scores for others. Clearly, this is a deliberate part of the program, due to the fact it it marking potentially wrong figures with a question mark (they're not all incorrect) - not that it is intentionally making mistakes, but I assume it is running some sort of optimization that speeds up the double dummy calculations rather than guaranteeing correct output. If this is required for some reason, why it does not at least switch to guaranteed correct output at least for later in the play when this should be fast, I also don't know. But at least I know more than I did.

No, it doesn't. You could have the last spade, and East the heart king, in which case a low heart results in -2 rather than -1. GIB cannot comprehend you bidding 3♣ with 22 HCP when it promises at most 18. (Sure, the other option has 19, but that's considerably more likely. And even if it considers both options, low is better at IMPs as long as it's 5:3 you have the more likely hand).

The point here is that if partner has 4 spades, they would bid 1♠ the first time. Bidding 1nt 100% guarantees that they do not hold spades. So if they then bid spades the next time, it's impossible that it actually shows spades, so a different meaning can be assigned to it. Specifically, it's used when you have a maximum hand with great support for partner's minor.

After you have played the hand, while it's still in your History panel, go to Export -> Send to Member, and send it to yourself. You can add a comment there, and it will show up in your mail box.

As you can probably guess partner held - 92 AQJT874 Q752 and the only making contract was 3♦. I did go the 3♠ - 4♥ route, though actually partner bid 4♣ over 3♠ which perhaps is a sign that you should give up and sign off in 4♦. Bidding is most likely right - I haven't run any numbers though I do wonder what the odds say in terms of the likelihood on finding a fit (and a fit may still not make game).

Originally IMPs, but it's probably an equally awkward (but interesting) question at MP too.

6-5 come alive, or stay low with a misfit? [hv=https://www.bridgebase.com/tools/handviewer.html?a=3DP&d=n&v=n&s=SAJ7542HAKT84D2C9]200|300[/hv]

Well, this still requires counting, just that you're now looking at how many cards there were above 6 to begin with, and then counting them down one by one each time one is played. But yes, my point was that you only need to be focused on a single suit.

If you're at the point where you have to take all the rest of the tricks but you're off one, it doesn't matter whether it's a part score, game, or slam - it can never hurt to cash all of your winners and see what happens. All you have to do here is pick one black suit - say spades - and count how many the opponents are throwing. At the end, if they've thrown too many, your small spade will be good. If they haven't, maybe they threw too many clubs, and your last club is good. They're squeezed if they're *forced* to do one of those things, but you don't even have to know that - as long as you keep both options alive as long as possible. Even when the opponents aren't squeezed, they may throw the wrong thing! (If you're not at that point of having to win all the tricks, and you can't see any way to get more, try losing tricks until you are.)

Ahha, so you're Ian ;) Not 100% sure about your second question, but try https://web.archive.org/web/20200130215544/http://orig.gibware.com/bidding/ .

The answer to this question is something you decide before opening 1♣. I know people open virtually all light hands these days, but I think I'd pass as opener.

How would these harm the double dummy score? You're measuring the difference between what you'd score if you got the number of tricks double dummy says you can, and what you actually scored. If your opponents the only ones bidding a grand that makes, the difference is 0 in this case - both double and single dummy give you the same score - so it doesn't harm or help. (I think you may be mixing it up with the *par* score which is something completely different.)

Richard Pavlicek's data here suggests that actual play results in slightly better than double dummy for everything except slams (and the biggest advantage is in NT contracts), precisely because of that lead factor. But not enough to boost those percentages for 3NT sufficiently.

Barmar has said in the past they deliberately don't publicize the number to prevent people from just logging in and out enough times to hit it. Many forum members are of the opinion that booting rights should be *more* locked down due to the number of people who abuse it, so it's not too strange an idea. Why you would need multiple accounts is possibly a stranger idea - while I am in no way suggesting this is what you are doing, there is a lot of potential for mis-use of this, so you'll have to live with the downsides.

More common is that 3♠ forces 3NT, with responder then able to show both 1 and 2 suited minor hands.

Yes, there is an unpublicised minimum number of logins required to boot players.

[hv=https://www.bridgebase.com/tools/handviewer.html?lin=st||pn|Frodo,Gandalf,GIBalrog,Sam|md|2SK2HAQJ5DA4CKJ982,SA86HK842DKQJ7C65,S954HT7DT98652CT4,SQJT73H963D3CAQ73|sv|e|rh||ah|Board%20112|mb|1D|an|Minor%20suit%20opening%20--%203+%20!D;%2011-21%20HCP;%2012-22%20total%20points%20|mb|P|mb|1S|an|One%20over%20one%20--%204+%20!S;%206+%20total%20points%20|mb|D|an|Two%20suit%20takeout%20--%204+%20!C;%205-%20!D;%204+%20!H;%205-%20!S;%2012+%20total%20points%20|mb|R!|an|Support%20redouble%20-%203%20S%20--%203+%20!D;%203%20!S;%2011-21%20HCP;%2012-22%20total%20points%20|mb|2H|an|4+%20!H;%2010-%20total%20points%20|mb|2S|an|The%20Law:%208%20trump%20-%3E%202%20level%20--%205+%20!S;%206-12%20total%20points%20|]400|300[/hv] Passing the opponents' support redouble is apparently illegal for GIB. (It will in fact bid 2♥ with a void in hearts if you give it 6070 and force this auction, though the opponents' sequence wouldn't occur).

18 total points, which adds to GIB's 18 to give 36 which it considers enough for grand. Without the redouble, North jumps to 6♦ instead.

Generally, you have a way of showing every balanced hand down to a narrow range: 12-14: open 1 of a suit, rebid 1NT 15-17: open 1NT 18-19: open 1 of a suit, rebid 2NT 20-21: open 2NT 22-24: open 2C, rebid 2N So there's no real need to increase the range of one of these bids - all that's going to do is decrease the range of another. *Responses* to your bid are far more wide-ranging, because of the gap between game and slam - if you're both balanced, it doesn't matter whether you have 25 points or 32 points, you're generally not going to want to go any higher than 3NT. (33 is typically what you want, though some hands are better than just their HCP). - If partner has a 7 count, partner is going to game when you show the 18-19 point hand anyway, so starting with 2NT with these won't gain anything. - If partner has a 3 count, you're better off starting low, and opening 2NT will cost you. - If partner has a 13 count, you'll be in a 31-32 point slam if you overbid initially - which on average will cost you. The main difference is the very small range where partner would do one thing opposite 20-21 and a different thing over 18-19 - those are hands where describing your hand accurately will result in a better score in the long run. Of course, some 19 point hands (eg ones with strong 5 card suits) are better than some 20 point hands - this is where upgrading comes into play. But once you decide how many points your hand is actually worth, then you bid it consistently based on the system, and leave the rest in the hands of your partner.