ChessBase Light 2007 - part 4

by ChessBase
6/15/2007 – Our Chessbase Workshop series which introduces you to the new ChessBase Light 2007 continues with a column devoted to interpreting the output of the engine analysis pane. Learn what your chess engine is really telling you in the latest ChessBase Workshop.

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Continuing our look at ChessBase Light 2007...

Another interesting feature of ChessBase Light 2007 involves the use of chess engines. A chess engine is more colloquially known as a "chessplaying program", but this is something of a misnomer when applied to CB Light. You can't play a game of chess against a chess engine in CB Light, nor can you use an engine to automatically analyze a complete game. What you can do is utilize an engine to analyze a particular position in order to receive the engine's opinion on the best course of play for both players.

The first step is to select a default analysis engine. ChessBase Light comes with a version of Fritz6. To select the engine, go to the Tools menu, select "Options", and click the "Engines" tab:


If you wish to change the default chess engine, click the "Browse" button (under "Default engine") and make a new selection.

After you've selected a default engine, you're ready to use one to analyze a position. As you're playing through the moves of a database game you can call on one of your chess engines to show you what it thinks is the best course of play after a particular move. Go to the Engine menu; you'll see two commands there for starting an engine:


The first "Add Kibitzer" command will also display the name of the engine you've selected as your default engine. The second "Add Kibitzer" command allows you to select any of the other chess engines you may have at your disposal. In most cases you'll click on the first command to start your default engine. After you've selected an engine you'll see a new pane appear on your game screen:


In this display you'll see two rows of buttons and informational boxes with a large pane located directly below them. This entire display is called the "Engine analysis pane". It's been described at length in previous ChessBase Workshop columns; consequently we won't go into complete detail here and will just cover the basics of what you'll need to know in order to understand it. Since we're discussing ChessBase Light, we'll consider this column to be "Engine pane instruction Light".

To understand the information included in this pane you must understand a bit of what a chess engine does as it analyzes a position, chiefly the concept of plies. We often talk about moves in chess, i.e. "I lost that game in forty-one moves". Let's consider a game in which Black resigns on his forty-first move. Each player made forty moves, White made his forty-first move, then Black resigned. Although we call this a "forty-one move game", we're actually talking about forty move pairs plus one extra move; in reality eighty-one individual moves have been made -- Black made forty moves while White made forty-one (40 + 41 = 81). Each of these individual moves is called a "ply" (sometimes called a "half-move" by people who are still stuck on the idea of a move pair constitiuting a "move" in chess).

Each time a player moves a piece, this is one ply. Let's assume a case in which a computer is analyzing a position in which it's White's turn to move. The chess engine looks at and evaluates each position following every legal move White can make; when this process is complete, the engine is said to have completed a search to a depth of one ply. Now it considers every legal Black reply to each of those White moves; when this is finished, the engine has analyzed to a depth of two plies. It now examines and evaluates every White response to each of those Black moves; after finishing, the engine has analyzed to a depth of three plies. I'm sure you get the idea (and, in reality, an engine can't analyze and evaluated all legal moves and replies, even on the fastest computers -- the "game tree" is just too vast. So it "prunes" the game tree by eliminating unpromising lines early in the search, i.e. moves which lose a large amount of material, or ones which give up too much board space, or ones which leave the King undefended. The risk is that the engine might overlook, say, a sacrifice which leads to an advantage many moves later, but it's a risk which must be taken due to the present technological limits).

Now that we've examined the concepts of "plies" and "ply depths", we're ready to look at the information provided in the engine analysis pane. We will, however, skip around the display just a bit to better organize the informational displays and buttons.

The button in the upper left corner displays the name of the engine you're using to analyze the position (in this case Fritz). Note that I did say this was a button; clicking on it brings up the same display that we saw earlier when we clicked on the "Browse" button to select a default engine -- so this button is a shortcut which lets you quickly change engines straight from the engine analysis pane.

Most of the boxes in this display provide you with information about where the engine currently is in its search. The "Depth=" box (third from left in the second row) shows you how deep (in plies; see above) the engine has currently searched. In the picture above Fritz is currently looking fourteen plies deep -- six full moves for both players, an extra full moves for White, and is now considering Black's replies to White's seventh moves from the original position.

The second box from the left in the top row further modifies the depth information. We see a move followed by two parenthesized numbers. The rightmost number in parentheses tells us how many legal moves are in the original position at which we started the engine -- in this case, there are thirty-one legal moves. The chess engine will assign an order to all of the legal moves, ranking them from most likely to least likely (or from "good" to "bad" if you will). We see that Fritz thinks that f3 is the best move so far; hence the "1" to the left of the slash in the parentheses. A few moments later I took another screen shot and saw this in the engine analysis pane:


See how the display has changed? Fritz is now considering the twenty-eighth of thirty-one legal moves (in this case Rxf7) and is analyzing out to a depth of fourteen plies. Note, too, that the "Depth=" number has changed to two numbers separated by a slash ("14/33"). This means that Fritz is analyzing fourteen plies deep in its brute force search, but is going much deeper (thirty-three plies) in its selective search -- a further "pruning" of the game tree in which an engine looks at forcing lines such as checks, captures/recaptures/exchanges, i.e. moves which force a specific kind of reply.

Note, too that the above graphic says "Stopped" instead of "Fritz" in the upper lefthand button. This brings us to the third box to the left in the top row -- this is actually a button which starts and stops the chess engine's analysis. The text in the box will change from "Stop" to "Go" (and vice-versa) depending on the engine's current state.

The second button in the second row shows the engine's evaluation of the current board position based on best play for both players. It will deliver the evaluation in two forms -- via an Informant-style notation symbol (which is explained in the program's Help file for those players unfamiliar with this symbolic notation), as well as in a numeric form, expressed in pawn units. A positive number means that White is better, while negative numbers mean that Black is better. This numeric display will "split hairs" right down to the hundredth of a pawn; for example, the above picture shows a numeric evaluation of "-0.28", meaning that Black is better by just over a quarter of a pawn.

The last button to the right in the bottom row lets you toggle between two pieces of information: speed (how many positions per second the engine is evaluating) or total number of positions evaluated so far in its present search. Both of these numbers are expressed in kilonodes (kN), i.e. a kilonode equals one thousand positions. In the graphic above for example, Fritz is analyzing at a speed of 992 kN/s -- that is, 992 thousand positions per second.

The first button in the second row is a "dashboard light" -- a warning which will turn red if the engine's evaluation suddenly swings by more than a full pawn in one player's favor. A red light appearing means that the engine has suddenly discovered a tactical shot which will, in most cases, mean that one player has a forced win of material or (in fewer cases) win a positional concession which is the equivalent of a pawn or more in the engine's evaluation.

If you're not an experienced user of chess engines, this information is an awful lot to digest -- and we still haven't finished looking at everything the engine analysis pane has to offer. We'll look at the main display of the pane in the next ChessBase Workshop and show you a variety of things you can do with it. Until next time, 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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