New Rybka analysis tools

1/25/2009 – One of the "old standards" in the area of positional analysis is the ability to show the next best move (or even multiple lines of play). But there's a "tradeoff": displaying multiple variations slows down the engine's analysis. The Rybka software contains a new feature which presents the user with more control over this process. You can learn all about it in our latest ChessBase Workshop.

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In the last ChessBase Workshop column we examined ways to decrease (or handicap) Rybka's playing strength. This time around we're going to consider ways of using Rybka as an analysis partner.

Rybka shares the positional analysis features you've come to expect in the Fritz/ChessProgram interface. But this new ChessBase engine brings some new features into the mix.

One of the "old standards" in the area of positional analysis is the ability to show the next best move (or even multiple lines of play). The best move/variation the engine finds will be displayed at the top of the list in the Engine Analysis pane. The user can then increase or decrease the number of displayed lines by use of the on-screen "+" and "-" buttons or the corresponding keys on the keyboard:

But there's a "tradeoff" at work here. Displaying multiple variations slows down the engine's analysis, sometimes to a significant extent when the user opts to display many of these alternative lines of play. And, as is the case with the illustration above, sometimes it's really not very fruitful to display these extra lines conidering how bad they are in comparison to the engine's preferred variation (the second and third best lines in the above illustration are more than a half-pawn worse than the preferred line in the engine's numerical evaluation).

The Rybka software contains a new feature which presents the user with a bit more control over this process. You can start a Rybka engine, right-click in the Engine Analysis pane, and select "Search options" from the popup menu to see the following dialogue:

There are several components to this dialogue. The box at the top (after "Number of mainlines") controls how many variations (maximum) will be displayed in the Engine Analysis pane. Checking "Evaluation window" enables the on-screen display.

The most important part of the dialogue in the unlabelled lower lower window. This allows you to set a margin, measured in 1/100ths of a pawn, within which secondary, tertiary, etc. variations must fall within (compared to the main variation) to be displayed in the Engine Analysis window. Let's explain this further by using an example. In the illustration above you can see the number of variations has been set at "2" and the margin has been set at "50". This means that two lines of play may be displayed, the best variation and the second-best line. But a second-best variation will be displayed only if it's evaluated as being worse than the main variation by a half-pawn ("50") or less; variations which are worse by more than a half-pawn won't be displayed at all.

The advantage here should be obvious; the Rybka engine won't waste processing power displaying and updating an on-screen variation if that variation isn't worth seeing in the first place. The dialogue shown above allows the user to set those parameters which the engine will follow, giving a display similar to what you see below:

The second-best line of play in the above illustration, evaluated at 22/100ths of a pawn worse than the main variation, is well within the half-pawn threshold we set in the configuration dialogue.

Note, by the way, that you'll need to set the "Number of variations" to "2" or more in the configuration dialogue, and that you should check the "Evaluation window" box to see those results displayed on the screen. (The box may seem redundant, but it's provided as a convenient "on/off" switch for users who don't want to continually reset the numerical values in the dialogue).

A second analysis option works somewhat "in reverse" of the dialogue we've just discussed. "Find better/Clearly better move" also searches for alternate lines of play, but instead of displaying lines which are x/100ths of a pawn worse than the main line, this feature searches for moves which are x/100ths of a pawn better.

I can hear you asking "Wait a minute -- if the engine is already displaying the best line of play (in its estimation), how can it display something better?" Here's a scenario to illustrate how this feature works.

Let's say that you're looking at a position and Rybka's analysis of a possible continuation. The engine is showing (as usual) the best line of play it's discovered so far. But you have a sneaking suspicion that there might be a better variation, which Rybka would find if it could look far more deeply at some possibilities it rejected early in the present search (perhaps a material sacrifice which was rejected because a short search did not reveal an advantage). So you right-click in the Engine Analysis pane, select "Next best", and then "Properties" from the submenu. You'll see the following dialogue:

This again allows you to set a margin, but this time the line displayed must be x/100ths of a pawn better than the previously-displayed main line (x being the value that you type into this dialogue's field). Click "OK" and when you activate the "Find better" or "Clearly better" dialogue, the software will cease to display the previous main line and will not display a variation in the Engine Analysis pane unless the engine finds a line which is better than the previously displayed main line by the value you set. Because the engine is no longer analyzing the previous main line and is instead searching for (sometimes radical) alternatives, it will look very deeply quite quickly and display any tactical solutions it might otherwise have considered "unpromising" and thus had pruned from the search tree early on.

Now I'll warn you straight away that this feature won't turn up a better move unless one actually exists, and this won't be the case in the majority of positions. But when it does find such a move, you might be blown away by the result. In fact, the programmers suggest setting a high value in this feature's dialogue in order to find any truly spectacular alternative variations which might lie hidden in the position.

Until next time, have fun!


© 2008, Steven A. Lopez. All rights reserved.


Topics: rybka3
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