5 INFLUENCING THE CHESS ENGINE

• 5.1 Changing the chess engine of REBEL
• 5.2 The different time levels under menu Levels
• 5.3 The other options under menu Option
• 5.3.1 Anti-GM (menu Option )
• 5.3.2 Engine (menu Option )
• 5.3.3 Permanent brain (menu Option )
• 5.3.4 Brute force (menu Option )
• 5.3.5 Combination (menu Option )
• 5.3.6 Selection (menu Option )
• 5.3.7 Playing style (menu Option )
• 5.3.8 Playing strength (menu Option )
• 5.3.9 Hashtables (menu Option )
• 5.3.10 Use EOC knowledge (menu Option )
• 5.3.11 Strongest settings (menu Option )
• 5.3.12 The ELO rating level (menu Option )

5.1 Changing the chess engine of REBEL

You can change the chess engine of the program in many ways.

Since the program always starts with the strongest settings, this means that every change you make will result in weakening the program.

5.2 The different time levels under menu Levels

At the start of the program, the playing level is taken from the last time you used the program. By changing the level of play, you can make the program stronger or weaker. The general rule is: the more time you give to the program, the stronger it will play.

Keyboards users use F2.

Overview



TIME (menu Levels )

          The program will play on the selected average time.



BLITZ (menu Levels )

          Play a game with a fixed amount of time. The program will warn

          you if you exceeded the time limit. In this case you have lost

          the game. You can see your remaining time in the time section.

         Choosing the last bar of the submenu will enable you to set

          your own desired time in minutes and seconds for a blitz game.



HANDICAP (menu Levels )

          Same as BLITZ, but now you can reserve more time for yourself

          and less for the computer. You can see your remaining time in

          the time section.





TOURNAMENT (menu Levels )

          Plays a game on a desired tournament level.

         Choosing the last bar of the submenu will enable you to set

          your own desired time in hours and minutes for a tournament game.



          The program will warn you if you exceeded the time limit. In

          this case you have lost the game.

          After the time control(s), you will receive the extra time

          needed. You can see your remaining time in the time section.



FISCHER BONUS (menu Levels )

          Gives you the possibility to play with the so-called "Fischer"

          clocks. The time you give here (0, 2 or user defined number of

          seconds up to 59) will be added to the time of the one who is

          moving at every time he or she makes a move.

          Fischer time level is only allowed at blitz, handicap or

          tournament level. The Fischer bonus time will be displayed in the

          upper bar of the move window.



PLY (menu Levels )

          Let the program play on a fixed (ply) depth.

          Besides the 9 fixed levels you can also choose in the appearing

          submenu to give your own number up to 60 ply.



MATE (menu Levels )

          A special level for solving difficult Mate problems.

          The program will ONLY search for a possible move sequence to

          achieve checkmate. If a mate is not possible at the current

          board position, the program will display: No mate possible and

          no move is being given by the program.

          Besides the 9 fixed levels you can also choose in the appearing

          submenu to give your own number up to 60 ply.



USER LEVEL (menu Levels )

          Same as TIME, but now you can define your own favorite level of

          play. You will be prompted to type the desired time. Type for

          example 00:00:25 and the program will play at an average time of

          25 seconds per move.





FIXED LEVEL (menu Levels )

          You can control the used time by second. If you enter for

          example 00:00:15, REBEL will always move after 15 seconds.

          This level is very suitable for the ever-increasing number of

          computer tests which are based on fixed times per move.

          HINT: This level is very useful together with Analyze database.



INFINITE (menu Levels )

          The program will continue evaluating until you stop it (i.e.

          with the REBEL button) or when a mate is found, or when the

          maximum ply depth is reached.



ANALYSIS LEVEL, ANALYSIS INCLUDE and ANALYSIS EXCLUDE

          For this special level we refer you to chapter 6.1 and 6.2.

5.3 The other options under menu Option

Menu "Option" contains a number of possibilities to change the chess engine of the program. Keyboards users use F3.

• 5.3.1 Anti-GM (menu Option )
• 5.3.2 Engine (menu Option )
• 5.3.3 Permanent brain (menu Option )
• 5.3.4 Brute force (menu Option )
• 5.3.5 Combination (menu Option )
• 5.3.6 Selection (menu Option )
• 5.3.7 Playing style (menu Option )
• 5.3.8 Playing strength (menu Option )
• 5.3.9 Hashtables (menu Option )
• 5.3.10 Use EOC knowledge (menu Option )
• 5.3.11 Strongest settings (menu Option )
• 5.3.12 The ELO rating level (menu Option )

5.3.1 Anti-GM (menu Option )

With this option activated Rebel will think his opponent is a GM (grandmaster) and will play differently. Rebel will try to be more humanlike and accordingly will play with more risks. This option was first activated during the match against Anand in 1998 where Rebel 10 scored 5 out of 8 games! Without this option, we believe Rebel's score would have been lower. You'll have 4 levels of anti-GM software to choose: none, active, strong and smart.

5.3.2 Engine (menu Option )

You can choose between four so-called chess-engines. By "engine" we mean that particular piece of software that makes REBEL calculate a move.

You can choose between the engine of REBEL 10.0 (standard loaded), Rebel 9.0, Rebel 8.0 and the engines that simulate REBEL 7.0 and REBEL DECADE. The ELO-rating that this engine is supposed to have on your particular PC will be changed automatically.

5.3.3 Permanent brain (menu Option )

With this option you can prevent the computer from thinking while it is your time to move. This will make the program weaker of course. If the permanent brain is active, the computer will take full advantage while you are thinking about your move.

5.3.4 Brute force (menu Option )

Brute force is a specific method for computer chess. If brute force is active, all possible positions will be evaluated, without regard to whether they are good or bad. The main advantage is that there is no risk that the computer will overlook a move. The default setting, however, is: "not active". The program will now use the selective method in which only the good moves will be evaluated. This will speed up the search time.

5.3.5 Combination (menu Option )

If Combination=ON (the default setting) the program generally will find the right moves in tactical positions faster than when combination is off due to a special tactical search. Combination=ON will find key-moves up to 10 times faster. The Combination=ON setting is also meant for popular computer test-sets. With Combination=ON Rebel will score better in these test-sets.

Note
The "combination" setting (ON or OFF) does not have any effect while playing normal games. When Combination=ON Rebel first will investigate if the current board position belongs to a game or if it is a position (game fragment). Only when Rebel discovers a position will the Combination=ON special tactical search be activated.

5.3.6 Selection (menu Option )

The program (when brute force is off) has its own intelligent flexible algorithm to decide if a given variation should be extended or not. This is called "selection" and is based on a judgement by the program whether it makes sense to extend a given variation or not. With this option you can turn off the program algorithm and change it into a fixed depth of selection. You will have the choice between 1 through 9. "N" is the default setting meaning Normal.

If you were to choose selective 4, while the program was, for example, on the 9th ply, this would mean that the calculations were done with the settings: 5 ply brute force and 4 ply selective thereafter.

With Normal the whole selection scheme is totally flexible.

5.3.7 Playing style (menu Option )

You have the choice of 5 different playing styles ranging from aggressive to defensive. In the pull-down menu the actual playing style is displayed by the corresponding uppercase letter.

5.3.8 Playing strength (menu Option )

There are 3 levels of playing strength. If you select the novice option here, you have the best possibility to beat the program.

In the pull-down menu the actual playing style is displayed by the corresponding uppercase letter.

5.3.9 Hashtables (menu Option )

The term hashtables stands for an algorithm in which the program stores the results of its evaluations into the PC memory.

This is very helpful for the program: when the program finds a position in the hashtable that was already evaluated, then there is no need to evaluate the position again since the result is already known.

This technique makes it possible to speed up the search process by a factor of three, and even more in the endgame.

At the start of the program, REBEL will try to reserve as much free memory as possible: the more free memory, the more positions the program can store. With this option you can change the size of the hashtables. Of course you cannot make the hashtable bigger than the size of free memory you have left on your computer.

5.3.10 Use EOC knowledge (menu Option )

Activating this option will enable REBEL to make use of the special EOC database that you have loaded during calculating.

The EOC (encyclopedia of chess) database is a re-compilation of Rebel's standard database of 300,000 high qualified chess games stored in a new super fast format. This enables Rebel to consult the database and based on what is found to adjust its play. Rebel can use the EOC data in two ways:

• Use as book: REBEL will search in the EOC database for the current position. If the EOC database contains this position REBEL will answer immediately with a next move found in the EOC database. We do not recommend this setting for optimal play but more as an option to study opening theory. The EOC database contains 16 million moves and its size is 20 times bigger than the standard opening book.
• Strong or active use: REBEL will search in the EOC database for the current position. If the EOC database contains this position, REBEL will look at the next move(s) in the EOC database and use in its calculations the result of these games by adding or subtracting some points to that move.

In this way REBEL will follow the human theory as represented in the EOC database of 16 million moves. The advantage above the EOC=BOOK setting is that the Rebel chess engine still is in charge and that major mistakes made by human players in the 300,000 game database are filtered by REBEL.

See section Load Encyclopedia for loading an EOC database.

5.3.11 Strongest settings (menu Option )

Using this function, you can restore Rebel's strongesr playing settings with one mouse click. If Rebel is already playing with the strongest settings, this menu item isn't selectable.

This option was introduced with the first Rebel 10.0 update version Rebel 10.0a

5.3.12 The ELO rating level (menu Option )

This is a very special playing level. With this level you have full control of the program's playing strength. Because of the ever-increasing playing strength of today's chess programs, it becomes more and more difficult to beat a chess program. When starting REBEL 10.0, the program quickly estimates the playing strength of the machine by checking the type and the speed of your PC. With this data, REBEL calculates an estimated ELO rating which can be found in Options. By changing this ELO rating (by clicking on it) you can lower the playing strength of REBEL. You can for instance type your own ELO. From this moment on you will have an opponent that is as strong as you are.

Some important comments:

• The system used by REBEL is of course not reliable to an exact ELO rating, however the goal of the system is more than sufficient.
• The ELO values used by REBEL are based on the FIDE standards. If you are used to USCF ratings, you must add 100-150 ELO points.
• The use of the ELO level of course makes no sense if you have already lowered the playing strength with other functions (for example with the novice option.)
• While playing a game with ELO level there will be NO additional information visible like main variations, hint moves or even book moves. Just like a real chess game, you are on your own.