Chess engines and evaluation function

Do all chess engines use the same evaluation function or is it different for different engines? I know there are two parts in that function:

1) material part -> 9*(#of queen)+5*(#of rooks) + etc.... ; this part, at least, should be the same for all engines

2) positional part; this is a question mark ....

Also can anybody suggest which way is better to reduce playing strength of Stockfish engine in Arena 3.5 : reduce rating or/and reduce playing strength in the engine configuration?

My guess is that the engines use different evaluation functions, but they won't be very different.

I would be interested to hear the definitive answer on this.

In Arena, to reduce the playing strength of Stockfish, you must change the playing strength in the engine configuration (0 to 20).

While you can change the elo rating of Stockfish in Arena, that elo rating is only an informational note to yourself - It is completely nonfunctional regarding the engine's actual performance. (You can test it for yourself. Set it to 3000, then set it to 100. It will perform exactly the same.)

Regarding your evaluation function question - I'm not a chess engine programmer, so I don't know the details. All I can do is point you to an authoratative source:

http://chessprogramming.wikispaces.com/Evaluation

Although, I'd imagine that the typical programmer would want to put his own "spin" on the evaluation function.

For your material suggestion, I'm pretty sure all engines don't use the same material point evaluations. I would have to look for specific references but I seem to recall that is the case.

Different engines use different evaluation functions. 

Thanks a lot! I was thinking the same way too. I entered a number 1700 into ELO box in the Engines-> Manage etc. but it definitely does NOT feel like 1700. I'll change playing strength to a lower number (say 50%-75%). By the way, did you have a chance to look into that EPD/FEN issue we discussed a while ago?

I don't even remember what it was about. (The benefits of getting older. :))

I'll try to find the thread to refresh my memory.

OK, now I remember. I guess I concluded that you're right, it's a bug. :)

One last question... When you analyze a position with Stockfish engine using Arena (either by pressing "Analyze" button or by doing automatic analysis) does engine analyze at maximum strength? You would expect it to...

Hmm, I don't know, I never tried that. I'd imagine it would analyze at whatever skill level it was set at. But it would be worth testing to know for sure.

I do know that I once did an auto-analysis with an engine that had multi-PV turned on, and it screwed up the auto-analysis bigtime.

Lets look at it the other way around: why would it NOT analyze at full strength? You would expect the best analysis you can get from an engine. Besides, I remember reading somewhere, what that reduced playing strength amounts to is a reduced amount of time an engine gets during a game while you on the other end of the board get full amount of time according to a chosen time control. Those levels (0-20) are percentage numbers 0%, 5%, 10% ......95%, 100% (in the increments of 5%), as I understand. When you analyze a position time does not have the same meaning. As far as automatic analysis is concerned, I remember I did automatic analysis several times with and without MultiPV and everything seemed to work both ways. That log file you get as an output is just an engine analysis written out into external file. By the way, it is normal that MultiPV slows engine down, so when playing a game against an engine you need to turn it off. But, I guess, it's a common knowledge for anybody who uses chess software on a regular basis

Rather than debate the hypothetical, I just ran a quick test. I was wrong and you were right. Reducing the skill level doesn't appear to slow down the engine in either manual or auto analysis. (I WAS just guessing, anyway.)

OK, enough of that playing strength. Going back to the issue of EPD files, I reminded you about it because I wanted to know if EPD files work in YOUR Arena. May be I got some demo/beta version of Arena and should download and reinstall it again. But then again, there's gray area with this free/open source software. You never know how to get in touch with people who developed software or whether they will answer your questions at all.

Yeah, I confirmed that the EPD bug is in my copy of Arena, too.