[sokaku]

Hello,
I'm a Chinese.
I'm just play with 3 robots.I don't know if they are GIB.
I loginned to msn,and enter bridgebase.then choose play with 3 robots.

The bug is:

Scoring: IMP

South play 4SX

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I am the south.
NS has got 6 tricks.
EW has got 3 tricks.
It is time for East to play.
It play H9,
I play SQ,
West play S3,
North play C7.
why west discard his trump S3 with my SQ?
I think this is a bug.
and i have met this serveral times.
That is,if Robot A want to trump a trick,and someone or robot B trump with
a bigger one before A,A will play the small trump, it waste its trump.

[Stephen Tu]

In the given layout, how is this a problem? GIB doesn't take any fewer tricks as long as it holds on to DA + CJ in the end game. Underruffing didn't cost it anything.

GIB basically tries to make plays that are percentage plays double-dummy based on random deals that match the bidding + previous play. If two plays are equal (here both spade + dq are equal), it will basically choose randomly.

This late in the end game, it rarely makes double dummy mistakes (shouldn't make any if all cards marked position), most of its defensive deficiencies are in the early/middle IMO mainly due to not having much concept of signaling other than count signals.

Underruffing is sometimes necessary on defense against certain layouts (admittedly rather rare), and sometimes just doesn't matter. It looks weird to you since humans will reflexively not do it, but unless it demonstrably can cost a trick vs. a possible remaining layout, you can't really classify something like this as a bug.