[Computer-go] issues on 19x19

Daniel Shawul dshawul at gmail.com
Wed Apr 27 08:23:41 PDT 2011

I am having problems making my engine play a decent game on 19x19 board.
Some KGS games
exposed the following problems.

1) Ladder problem. It often mis-evaluates ladders despite my best efforts to
detect them
in the playouts. So I resorted to doing qsearch at the root to weed out
moves which
loose tactically, and make winning moves immediately. That helped but
sometimes the qsearch explodes and engine looses on time.
I tried putting a limit to the depth of qsearch but it still runs into
problems. Using a small depth limit may
help in 9x9 but on 19x19, atleast 40 plies is required to detect one ladder
along the diagonal... so what to do ?

2) My second problem concerns use of progressive widening/unpruning which
looks like a must to have on 19x19.
The problem I have is with the move ordering... If I tell it to  moves on
the 3rd line from the edge are good ones,
it continually puts its stones on that line (hence forming a square), while
the opponent controls the centre and also
cuts some parts of the 3rd line.
Then I used fillboard to try and fix this issue, but the engine once again
tends to prefer these moves and put stones
all over the board. Which is when I realized it is impossible to fix it with
static move ordering.
Should I use something dynamic like RAVE to order the moves? That will be
inconvinient  because I order the nodes
only during first allocation.
Also the default progressive unpruning formula seems to select too few moves
for consideration, so I had to add 20 additional moves
to make it work for my engine.
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