is a game by Christian Freeling. Java applet © 1997 Ed van
Zon.
Caïssa is a sort of chess game that was published
first on www.mindsports.net.
See here
for the playing rules. I competed with an own version at the CodeCup
2003. My program is called HIPP and is made in C. You can download
a project version and study it. For the calculation of the best
move HIPP uses the MTD(f)
algorithm. This algorithm uses the constant calling of alfabeta
pruning (without memory function) with a so called zerowindow
search. I have limited the range from the evaluation function
from 25 tot 25 to reduce the number of calls. The algorithm is
called iteratively to calculated a move one step deeper each time.
In the beginning it is not necessary to check for the connection
rule and HIPP searches four levels deep. In the endgame the connection
rule needs to be checked and HIPP searches for three levels deep.
After a quicksort of the possible moves HIPP calculates the best
five moves one step deeper. By using a fast generator for moves
HIPP finds for each position in the beginning ± 3 million
moves. About 30.000 moves are actually executed and 27.000 positions
are evaluated. That takes about ± 3 seconds. I have implemented
more ideas and I have descibed them in a PDFdocument. You can download
the document, print and read it. A short summarize:
 If in a certain position check is given, HIPP calculates
one step deeper from that point because in such a situation
the number of countermoves is limited. If in the beginning game
two or three moves are available the situation is also calculated
one step deeper. Due to this a checkmate situation is found
at ten levels deep. In this way I guess that HIPP searches effectively
for six to seven levels deep.
 The basic idea for the evaluation function is simple and
fast: Value= NumberMovesOfMyself  NumberMovesOfOpponent. For
this the number of moves from the opponent from the called level
is used. I have a big advantage if my opponent is given check!
 The first four moves from white and the first three moves
of white are calculated in advance. The making of the opening
book took about three weeks on a 850 MHzmachine. By calculating
the opening moves by more than ten levels deep secures a safe,
fast and favourable opening.
