Engines fail to find mate in two

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John Upham
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Engines fail to find mate in two

Postby John Upham » Mon Nov 07, 2016 11:11 am

Here is a question for the engine buffs out there (I don't know the answer).

I put the following position into Fritz 13 and without any prompting it could only find various mates in three.

When I manually played 1 Rb7! it then found the various mates after 5 different moves by Black.

Maybe more modern engines do not have this problem?

Pos1.jpg
Pos1.jpg (46.88 KiB) Viewed 1165 times

LawrenceCooper
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Re: Engines fail to find mate in two

Postby LawrenceCooper » Mon Nov 07, 2016 12:19 pm

The same (not surprisingly) with Fritz 11.

John Upham
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Re: Engines fail to find mate in two

Postby John Upham » Mon Nov 07, 2016 12:26 pm

Curious...

Anyone have an explanation for this?

I assume that from my given starting position all possible (45?) legal moves for white would be tried by the algorithm.

I understand that engines can fail to assess a number of simple positions correctly due to a horizon limiting effect but missing mate in two cannot have this explanation surely?

Brendan O'Gorman
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Re: Engines fail to find mate in two

Postby Brendan O'Gorman » Mon Nov 07, 2016 12:35 pm

Komodo 10, Stockfish 7 and Deep Hiarcs 14 all find the two move mate instantly. I inadvertently set up the position the wrong way round initially, i.e. with White playing down the board. That turned out to be a mate in three.

MartinCarpenter
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Re: Engines fail to find mate in two

Postby MartinCarpenter » Mon Nov 07, 2016 12:38 pm

Engines will sort of look at all moves, but they do also have built in algorithms to stop them chasing down blind alleys.

That was especially so with older ones, because their hardware was more limited & so the cost/benefit ratio of limiting the search was rather higher. I have a vague memory that way back they had 'puzzle' modes that turned these things off to make sure of catching all of this.

Quite why Rb7 is being cut away here I'm not sure, as it definitely isn't an a priori nonsensical move. Easier to see it with longer searches and massive sacrifices and things.

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IM Jack Rudd
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Re: Engines fail to find mate in two

Postby IM Jack Rudd » Mon Nov 07, 2016 12:39 pm

Houdini 4 finds it instantly.

John Upham
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Re: Engines fail to find mate in two

Postby John Upham » Mon Nov 07, 2016 12:45 pm

IM Jack Rudd wrote:Houdini 4 finds it instantly.


Thanks Jack!

Does this mean that this is a well known problem that has been addressed with the more recent engines and I need to go shopping?

John Moore
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Re: Engines fail to find mate in two

Postby John Moore » Mon Nov 07, 2016 5:06 pm

John, I'd send it off (the position, not the engine!) to ChessBase and ask for their comments. Fritz 13 is hardly an old engine. Tell them you purchased it in good faith and yet it can't do a mate in 2 and see what they say. Then report back here.

Nick Grey
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Re: Engines fail to find mate in two

Postby Nick Grey » Mon Nov 07, 2016 6:59 pm

John, you've been sold a pup.

Ask for an explanation & more than that. Obviously cannot be good for them compared to their competitors.

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Re: Engines fail to find mate in two

Postby John Upham » Mon Nov 07, 2016 7:18 pm

Nick Grey wrote:John, you've been sold a pup.

Ask for an explanation & more than that. Obviously cannot be good for them compared to their competitors.


The current version is Fritz 15. I'm not after a refund or recriminations about a product which was released more than six years ago.

The modern engines find the mate without prompting.

As a developer I am curious as to the "bug" that we have discussed.

The offside window in my more than ten year old VW Golf dropped into the door cavity but I don't feel the need to complain to VW about it. Some might I suppose.

E Michael White
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Re: Engines fail to find mate in two

Postby E Michael White » Mon Nov 07, 2016 7:33 pm

My version of deep Fritz 12 finds Rb7 immediately, as do Fritz 6 and Crafty 23.01.

Nick Grey
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Re: Engines fail to find mate in two

Postby Nick Grey » Mon Nov 07, 2016 7:40 pm

It is something we might want to test before upgrading or buying new product. Almost like the Bond film where the villain deliberately issues software with bugs in it & then charges customers to fix it.

On the development side of the old programme may well be patzer sees a simple mate in 3 that ends the game & does not want to consider whether there is a quicker way bearing in mind the same result 1-0.

More human like response from Fritz. My old Fritz 6 was working really well until my children started to mess around with the programme settings to see how quickly they could beat the computer.

Mind you it has been a long time since I was 2 rooks, 1 queen, & 1 pawn up and my opponent had not resigned.

John Moore
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Re: Engines fail to find mate in two

Postby John Moore » Tue Nov 08, 2016 7:26 am

John Upham wrote:
Nick Grey wrote:John, you've been sold a pup.

Ask for an explanation & more than that. Obviously cannot be good for them compared to their competitors.


The current version is Fritz 15. I'm not after a refund or recriminations about a product which was released more than six years ago.

The modern engines find the mate without prompting.

As a developer I am curious as to the "bug" that we have discussed.

The offside window in my more than ten year old VW Golf dropped into the door cavity but I don't feel the need to complain to VW about it. Some might I suppose.


I was being slightly tongue in cheek with my comment up thread and I certainly wasn't suggesting that you should seek a refund when you have been using it for six years (!) but it would have been interesting to see the response from ChessBase. After all, they might be able to satisfy your curiosity.

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Re: Engines fail to find mate in two

Postby Mick Norris » Tue Nov 08, 2016 8:31 am

John Upham wrote:The offside window in my more than ten year old VW Golf dropped into the door cavity but I don't feel the need to complain to VW about it. Some might I suppose.


German engineering :roll:
Any postings on here represent my personal views and should not be taken as representative of the Manchester Chess Federation www.manchesterchess.co.uk

Kevin Thurlow
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Re: Engines fail to find mate in two

Postby Kevin Thurlow » Tue Nov 08, 2016 8:46 am

"Almost like the Bond film where the villain deliberately issues software with bugs in it & then charges customers to fix it."

Sounds like real life to me!


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