by Steve Lopez

Almost anyone who's used ChessBase 8 for more than about ten minutes is familiar with the standard analysis engine display, in which the engine shows the best line of play it's found in the current board position:

And, of course, you can increase the number of lines displayed (thus showing the second-best, third-best, etc., moves that the engine finds) by clicking the "+" button in the engine analysis pane, or decrease them by clicking the "-" button in the same pane. But there's an additional display form that's pretty interesting for seeing how the engine "changes its mind" as its search deepens. Right-click in the engine analysis pane and select "Scroll main line" from the popup menu. The engine analysis pane will change to display the following:

In the standard analysis display, the engine updates the display with new moves or a new evaluation and replaces the former moves/evaluation with the updated version. In this new display (after selecting "Scroll main line") the engine doesn't replace the former moves/evaluation; instead, it adds a new line to the engine pane each time it changes either the positional evaluation or a move in the best variation it's found so far. For example (in the graphic above), it added a second line when it changed the positional evaluation from 4.66 to 4.56. The evaluation stays the same in the third line, but you'll note that White's thirteenth move has changed in the variation that the engine is suggesting. In the fourth line of the display, the variation has stayed the same, but the engine has reevaluated the position (from 4.56 to 4.47).

While this display form is certainly interesting, it's not terribly informative in terms of when the engine changes its evaluation. You can get this information by right-clicking in the engine pane again and selecting "Extra search info". This alters the engine analysis display yet again:

The difference here is that the engine now adds a new line each time it completes a ply of the search; i.e. when the search depth is increased by one ply (half move), a new line is added to the display. In the graphic above we see the engine's analysis after it has completed an eight ply search, a nine ply search, a ten ply search, an eleven ply search, and a twelve ply search. We can see at a glance how the engine's evaluation and suggested line of play has changed with each one ply increase to the search.

But there's some additional information provided as well. Not only can we see the exact points at which the evaluations/variations change, but we also get a lot of useful extra information too. Let's use the information for the first variation as an example and explain what each of these entries means.

The first symbol to the left is the standard Informant-style notation for the positional evaluation at the end of the variation the engine suggests. In this case it's "+-", meaning that White is winning. After that is the numerical evaluation (in pawn increments, with a positive number meaning an advantage to White and a negative number meaning that Black has the advantage); in the case of this example, White is leading by four and sixty-two 100ths pawns. Next is the search depth information; "8/21" means that the engine has completed an eight ply brute force search (in which it analyzes nearly all moves and replies out to a depth of eight half-moves) and a twenty-one ply selective search (meaning that it's analyzed promising or forcing lines of ply out to a depth of twenty-one half moves).

We next see the amount of time it took the engine to reach the ply depth in question and come up with the suggested variation. In this case "00:00:00" means that the engine did an eight ply search nearly instantaneously. (And this is some really valuable information when you're gauging the speeds of different chess engines. Skip down to the bottom of the display, where the engine shows what it was "thinking" after a twelve ply search; we see that it took the engine forty-six seconds to decide on its recommended variation).

Finally we see the number of unique positions the engine evaluated at each ply of the search (and the term "unique" here means exactly that -- transpositions previously stored in the engine's hash tables aren't counted in this figure). This figure is given in kilonodes, meaning thousands of positions. After a near-instantaneous eight-ply search, the engine examined 55,000 unique positions. In reaching twelve plies, the engine evaluated 3,282,000 positions.

This is a lot of useful information, but some users may find this to be a case of "information overload". There is a "middle ground" though. Right-click in the engine analysis pane and select "Scroll new moves only" from the popup menu. Now a new line will be added to the display only when a variation starting with a new move is preferred by the engine:

Additionally the engine will also update the extra information given below the variations. In the graphic above, we see that the engine initially preferred a variation starting with 11.Bd3, but between one and two seconds into the search it changed its mind and preferred the variation starting with 11.dxc7. It stayed with that variation into the twelfth ply but changed its mind again (to the 11.Na3 variation) at 4:25 into the search. It sticks with that variation well into the fourteenth ply (over twenty-one minutes into its search). Note, too, that the engine has evaluated over 115,000,000 unique positions at this point.

This last display gives you a lot of useful information without piling on a lot of extra (and possibly extraneous) info. Ultimately the choice is up to you; just right-click in the analysis pane to explore these options and find the display setting that you find the most useful.

As a side note, you can't drop all of this information into the gamescore by right-clicking in the analysis pane and selecting "Copy to notation"; only the best line found so far will be copied into the notation pane. However, you can right-click in the analysis pane, select "Clip analysis" (to copy the full contents of the analysis pane into the Windows Clipboard), open a text annotation window (CTRL-A), and then hit CTRL-V to paste it all into that annotation window. The moves won't be replayable in the chessboard window (as they are after "Copy to notation") but you'll preserve the additional information as to the changes the engine made in its analysis at various points in the search.

Until next week, have fun!

You can e-mail me with your comments, suggestions, and analysis for Electronic T-Notes.