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Does GIB pick a random card when making opening lead?

#1 User is offline   wbartley 

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Posted 2018-March-01, 13:19

Just Play Bridge robot. Human South.



I tried to add the T play into my diagram but it didn't stick when I inserted. Apparently the hand editor can only handle a full round or something.

Anyway. GIB led the T.

If GIB isn't just randomly selecting a card, what logic is it using? Does anyone know? Even if it decides, for whatever reason, that hearts is the best suit to lead, surely leading the ten from T8x in the blind can't be right. If the code that decides what suit to lead is so sensitive and unintelligible as to strike fear into the heart of anyone thinking of modifying it, at least changing which card it leads from Txx in the blind shouldn't be too difficult.
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#2 User is offline   steve2005 

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Posted 2018-March-01, 13:38

Just play bridge Gib may not make best defense.
But BBO seems to be very sensitive about Gi's leads. Insisting that we should read the book (read the book Winning Notrump Leads to understand.
I'm sorry but when you partner opens a weak 2 and the opponents get to 3NT and Gib with nothing special doesn't lead the preempt suit it's time read a different book.
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#3 User is offline   Stefan_O 

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Posted 2018-March-01, 17:02

Gib is supposed to use randomized double-dummy analysis. Both for first-trick leads as well as for the subsequent cards played.

What this means, is that it will generate a number of (semi)random deals, but deals consistent with the bidding and play up to the current point in the deal.

Whatever layout it analyses, it will assume everyone is playing double-dummy and select a card that will on average give the best result over the sample of random-deals it has generated and analyzed.

It will not take into account any "psychological" factors, etc, or the fact that a certain play would give opponent a guess or not.

Incidentally, on the example deal you give, double-dummy, a low heart is just as bad as the ten (since declarer will duck the lead in dummy -- double dummy, remember!), so even if this exact deal would have been part of the randomized sample of deals generated and analyzed, it in itself would not have given Gib any guidance as whether to lead a low heart or the Ten.
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#4 User is offline   Stefan_O 

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Posted 2018-March-01, 17:50

Here one spectacular "what could possibly go wrong" example,
of Gib picking a "random-card" when "it doesn't matter" double-dummy:

http://www.bridgebas...882-why-does-gi
b-defender-always-play-highest-of-equals/page__p__940482__fromsearch__1
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#5 User is offline   smerriman 

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Posted 2018-March-01, 18:00

You might like to read this post, where I prove that there are indeed times where GIB simply leads randomly, against the documentation and not even possibly based on simulations.

This is my favorite example - GIB is programmed to lead high from a doubleton, unless a simulation tells it another card works better. I wonder what hands it simulated to achieve this lead:


Feel free to send me a friend challenge of any format as often as you like. I'll always accept :)
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#6 User is offline   steve2005 

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Posted 2018-March-02, 10:43

View Postsmerriman, on 2018-March-01, 18:00, said:

This is my favorite example - GIB is programmed to lead high from a doubleton, unless a simulation tells it another card works better. I wonder what hands it simulated to achieve this lead:


Wow Gib figured out double dummy it doesn't matter what card it plays, so played randomly. <sarcasm>
Yes Gib defense at times is worse than someone who learned the game that day.

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