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You'll recall from the previous two ChessBase Workshop columns that we've been examining the use of chess engines in CBLight. In this column we'll look at a few more engine-related features that you'll doubtless find useful.
As a chess engine analyzes a position it will display the best variation (or variations -- see last week's column) it has found so far. The top variation assumes best play for both sides (that both players are making the best possible moves -- in the engine's "opinion", of course). But how can you see these moves played out? Do you have to try to play them "in your head" without moving pieces on an on-screen chessboard?
Of course not. There's a special feature called the "Variation board" which will allow you to play out the best line of play which the engine has found so far. It will provide a small additional chessboard on which you can replay the top variation.
There's a prerequisite which must be met before activating the variation board: your monitor must be set for a display resolution of at least 1024 by 768 pixels. Almost all present-day monitors are capable of operating at this resolution. To check or change your monitor's resolution, right-click on your Windows desktop, select "Properties", and then click on the "Settings" tab. You'll see a slider which allows you to set your screen resolution.
After you've checked (and changed if necessary) your screen resolution, you'll be ready to use the variation board. Fire up an engine and right-click in the engine analysis pane:
You'll see a command called "Variation board". Click on it to activate the board, which you will see appear as part of the engine analysis pane:
When you call up the variation board, the first move of the engine's preferred line will already be displayed on the variation board (e.g. the move will already have been made on the small board); it's a simple matter to compare the position on the main board against the one on the variation board to see the "before and after". It's also interesting to note that the variation board's initial position will change automatically in the event of the engine changing its mind and coming up with a different first move later in its search.
But how do we make the additional moves of the engine's preferred line appear on the variation board?
Notice a set of buttons below the variation board. These "VCR" buttons allow you to step through the moves of the engine's preferred variation. The "single arrow" buttons step forward or backward through the variation one move at a time; the "right arrow" button moves forward through the moves, while the "left arrow" button goes backwards (i.e. takes moves back). Just click on a button and the pieces on the variation board move to reflect the new position.
The "double arrow" buttons jump the board position directly to the beginning or end of the engine's top variation. The "double right arrow" button takes you immediately to the end of the variation while the "double left arrow" goes directly back to the first move of the variation.
As the engine progresses more deeply into its analysis process, it will naturally change the displayed variation as it finds better moves. The operation of the variation board will automatically reflect this; you'll always be playing through the current best variation on this small board. Since the engine will usually frequently "change its mind" early in the analysis process (and thus change the contents of the variation board), it's probably best to wait a while for the engine to settle down a bit before launching the variation board.
If you've finished using the variation board and want to hide it, just right-click again in the engine analysis pane and select "Variation board" a second time. This will remove the variation board from the pane.
Another useful engine feature which can be accessed by right-clicking is "Analyze threat". To understand the output of this feature, we must first define a "threat". I've read a lot of high-flown definitions of the term "threat" in chess books and more than a few writers seem to miss the woods for the trees by overcomplicating their definitions. Simply put, a threat is what a player would do if he were allowed to make two moves in a row. That's it -- there's nothing complicated about it.
When a player makes a move which establishes a threat, he's requiring his opponent to make a move which stops or neutralizes the threat. If the opponent makes some other move (because he misses the threat) and the first player follows through on the threat, it's as though that first player had indeed made two moves in a row: the first move created the threat while the second move carried it out.
When you right-click in the engine analysis pane and select "Analyze threat", you'll see the engine start analyzing the position from the point of view of the side which just moved -- in other words, it will act as if the moving side is about to make a second move in a row. After all, that is the definition of a threat, right?
Let's look at a really simple example. In the following position, Black has just played 56...Nc3:
Next we'll start the engine's analysis; of course we'll notice that the variation begins with a White move since it's White's turn:
But watch what happens after we right-click and select "Analyze threat":
The engine display changes and the variation it shows now begins with a Black move. It's displaying the threat: what Black would do if he could move twice in a row. And in this instance it's the very obvious 57...Nxb1 (I told you this would be a simple example). But not every threat is as obvious as this one; "Analyze threat" is a great (but often overlooked) tool for answering the often-asked question, "Why did he play that?"
I'll have more on ChessBase Light 2007's engine functions in the next ChessBase Workshop. Until then, have fun!
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