Infinite analysis

by ChessBase
6/8/2007 – In the new ChessBase Workshop, our columnist revisits an old Fritz feature, Infinite analysis, and offers a new spin on it suggested by our readers. We also examine the related (and often misunderstood) "Lock engine" command. Learn more in the latest Workshop.

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I recently received a couple of e-mails which I thought were fairly interesting; two separate people were asking the same question (more or less): how to use the "infinite analysis" feature of ChessBase/Fritz/etc. to analyze a complete game.

Longtime users of these programs might be taken aback by that question (as was I); there are three other analysis modes available for analyzing complete games, and Infinite analysis is designed to provide "on the fly" analysis for single moves, not whole games. One of my correspondents went on to elaborate: he wanted to fully control the process, letting an engine analyze for a long period on particular moves but for just a short time on others.

I understand what these users are doing and, although I'm not advocating the technique for every user (I'll stick with the Blundercheck and "Compare analysis" modes myself), I thought it was worth a closer look in ChessBase Workshop. It'll also give us an opportunity to examine a couple of Fritz' features.

Let's start by describing the "Infinite analysis" mode itself. As I stated above, it's a means of getting "on the fly" analysis of particular individual moves without taking the time to have an engine analyze the complete game. Here's an example -- we're reviewing a game from the database and come across the following position:


To start infinite analysis mode in the Fritz10 interface, go to the Engine menu and select the Infinite analysis command. It will appear in the menu as "Infinite analysis:" followed by the name of the engine you've selected as your default engine (Engine menu/"Change main engine").

The engine analysis pane will spring to life and show you what the engine is "thinking":


The part of the display we'll need to keep an eye on is the "Depth:" value. The number to the left of the slash is the number of plies (half-moves) deep the engine has searched in its brute force search, while the number to the right of the slash is the depth (also in half-moves) in its selective search.

How deep should you let the engine search? That's entirely your choice -- it's really a matter of how long you're willing to wait. The feature is called "Infinite analysis" for a reason -- in this mode, an engine will analyze a position until some external force (you, a computer crash, a power outage, etc.) stops it. In theory, an engine could examine a single position forever in this mode.

I've heard of some grandmasters who've let this feature run on a single position for hours overnight (I believe Garry Kasparov even mentions this in an old ChessBase Magazine interview, as I recall). But we're discussing the process of having an engine analyze an entire game manually using the "Infinite analysis" feature, so letting an engine look at a single position overnight just isn't an option here.

So, in short, it's your decision as to when to stop the engine. My personal opinion is that anything less than twelve plies on modern hardware (PIII and up) should be considered rather cursory. Be aware, though, that you're not going to reach forty ply depths on a typical PC (at least not in a time frame which you're willing to sit and wait out), so you'll need to find a happy medium.

There are two tools which you'll find very handy, whether you're analyzing a whole game or a single position. Both are accessed by right-clicking within the engine analysis pane:


The first is "Lock engine". This is a frequently misunderstood command; some users think it pauses an engine's analysis and allows it to be restarted later. That's not so. Under normal conditions while an engine is running in "Infinite analysis" mode, the engine will continue to analyze a position until you move to another position in the game -- then the engine "drops" (or "loses", "forgets", etc.) the analysis of the old position and immediately begins to analyze the new position on the chessboard. The "Lock engine" command prevents this from happening. When you lock the engine, it will continue to analyze the former position even after you move to another position in the game. Obviously, this is a really handy feature. You can let Fritz (or another engine) keep analyzing a position while you move around in the gamescore, possibly looking for the next position you wish to have the engine analyze. (In fact, I think that's a useful technique for manually directing an engine's analysis. Instead of having an engine analyze every single move in a game using "Infinite analysis", you can look for a few crucial points in a game to have the engine consider and, by using "Lock engine", even search for these positions during the analysis process).

The second is "Copy to notation". This takes the present content of the engine analysis pane (i.e. the best variation found so far in the search) and drops it into the gamescore as a replayable variation:


In addition to the replayable variation, you'll also see the name of the engine which generated the analysis, the evaluation of the position (in hundredths of a pawn), and the brute force search depth (in plies). We see in the above illustration that Fritz10 generated the analysis, that White is 0.11 pawns ahead, and that the search was fifteen plies deep.

If you wish to save this information as a part of the gamescore, don't forget to go to the File menu and select "Replace" -- otherwise the engine-generated commentary will be lost after you load another game or exit the program.

As I said earlier in this column, I'm not sure that I'd want to analyze a complete game in this manner (manually directing an engine through the process), but if you have just a few positions which you're curious about in a game and wish to see what an engine "thinks", I believe this is a great technique to use -- not only to get answers but to preserve them (by using "Copy to notation").

Until next week, have fun!

You can e-mail me with your comments on ChessBase Workshop. All responses will be read, and sending an e-mail to this address grants us permission to use it in a future column. No tech support questions, please.

© 2007, Steven A. Lopez. All rights reserved.


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