I’ve had a couple of interesting conversations lately with users of the Fritz “family” of playing programs (Fritz, Rybka, Hiarcs, Junior, and Shredder) who weren’t quite sure what “Infinite analysis” does, or, in one case, what it can do for them. “Infinite analysis” has a lot of uses, all based on the idea that you feed a position to the chess engine and let it chew on the position to find the best sequence of play. It’s not terribly different from the way we human analyze when we’re playing a face-to-face game: we try to figure out the best move, followed by our opponents’ best reply, followed by what we’d do next, etc. – it’s the old “If I do this, he’ll do this, then I’ll do this…” thing. The difference is that a chess engine will look much farther ahead (“deeper”) than any human could do, as well as pick better moves than we average players would normally choose.
The value of this feature should be instantly apparent: in home analysis we can double-check our own ideas to determine their validity. If I come up with something I think might be a “novelty” in an opening I play, I can use a variety of chess engines to look for “holes” in my thinking or responses I might have overlooked. In fact, many top-level chessplayers check their homebrew analysis in exactly this way. About fifteen years ago, Garry Kasparov was quoted in ChessBase Magazine as saying he used Hiarcs in “Infinite analysis” mode to double-check theoretical novelties before he introduced them into professional play.
Why “Infinite analysis”? And why is it called that?
Infinite analysis gets its name from the fact that the engine will analyze a position until you stop it, in other words, infinitely (at least in theory). You could take a opening position and have Fritz/Rybka/etc. analyze it for an hour, a day, a week, a month, and (barring power outages or other mishaps) when you come back to the computer the engine will still be analyzing that position. And why would you want an engine to analyze for an extended period? As we’ve learned in previous blog posts, the longer you allow a chess engine to analyze a position, the better the moves you will receive in return.
Let’s look at a simple practical application. I’m looking at an opening variation in a chess book, a variation from the Ruy Lopez Worrall Attack: 1.e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Be7 6. Qe2 b5 7. Bb3 O-O 8. c3 d5 9. exd5 Bg4 10. dxc6 e4 11. d4 exf3 12. gxf3 Bh5 13. Bf4 Re8.
The book’s evaluation is that Black has counterplay in exchange for the lost two pawns after his thirteenth move. I’d like to test that assertion using Shredder12 as the analysis engine. There are a number of different ways we can tackle the task; the simplest would be to just click on the last move in the notation pane to highlight it:
and then launch “Infinite analysis” from the “Home menu”:
then let the engine run for a while to see its analysis in the Engine analysis pane:
But I’d like to show you something a bit more elaborate which will allow you to save the engine’s analysis as part of your database.
After entering and saving the variation line shown above, I’ll click on the variation’s last move and then hit the “T” (takeback) key on the keyboard. This takes back the final move and allows me to enter another move as a variation. In this case, I’ll enter the same move again, which will now appear as a variation line:
Now I’ll click again on the last move of the main line, go to the “Home” menu, and click the “Infinite analysis” button to start Shredder12. Since this is Infinite analysis mode, I don’t have to fiddle with time or depth settings; the engine will run until I manually stop it. So after starting the engine’s analysis, I can just go away and do something else for a while to let the engine analyze…
Later, after I come back and am satisfied with how deep the engine has searched, I can right-click in the Engine analysis pane and select “Copy to notation” from the popup menu:
This will copy the best line of play (for both players) to the game’s notation:
And now we have one more important step (which will also explain why we created another variation by using the “T” key earlier). I’ll right-click on the single-move variation and select “Promote variation” from the popup menu:
…and we see that the main line and the variation have “switched places”:
…after which I can use “Replace game” to save the analysis into the database. Since Shredder12’s analysis has been copied to the notation, I can play through it to closely examine what the engine thinks are the best moves for both players; in other words, I’m not getting only the best move for White in the original position, but I’m also seeing how Shredder thinks the game should progress thereafter.
So why go through all the trouble of adding an extra variation and then re-sorting the variation and main line? I have two reasons. First, the main line is still the original variation as I found it in a book. Second, following this procedure makes it easy for me to have another chess engine (or multiple engines, should I choose to continue to repeat the procedure) analyze the same position and give its opinion of what should occur next:
Comparing the analysis of two or more engines is a handy way to confirm a particular course of action in a given position.
The amount of time you should allow Infinite analysis to run is totally up to you. Kasparov (and other top players who’ve publicly discussed the technique) let the engine run overnight. Bear in mind, however, that each ply (move) added to the search depth exponentially increases the number of positions which the engine must evaluate; there will quickly come a point where it can easily require an hour or more to add just one extra ply to the search. So the trick is to find the happy medium in which you’re satisfied with the depth of the search compared with the time required to produce the result.
Have fun! – Steve Lopez
Chessplayers who have purchased their ChessBase brand chess computer software from USCFSales can receive free technical support and advice on their purchases straight from me; just shoot me an e-mail (firstname.lastname@example.org), but please remember to include the USCFSales order number from your ChessBase software purchase. – Steve
Copyright 2011, Steven A. Lopez. All rights reserved.