On Jan 14, 2009, at 9:36 AM, Daniel Waeber wrote:
I have a question about the the part were the stats are updated.
(l.15-25). having an array of amaf-values in every node seems very
memory
intensive and I don't get how you would access these values.
You are right, it is memory intensive. I believe this is one of the
reasons that most implementations wait a certain number of playouts
before creating the next level of nodes.
Accessing the AMAF values depends on your implementation. The
following is a code-snippet from my MCTS reference implementation that
updates the AMAF values in the tree:
if (_useAMAF)
{
IntStack playoutMoves =
_searchAdministration.getMoveStack();
byte color =
_monteCarloAdministration.getColorToMove();
int start =
_monteCarloAdministration.getMoveStack().getSize();
int end = playoutMoves.getSize();
double weight = 1.0;
double weightDelta = 1.0 / (end - start + 1); // Michael Williams'
idea to use decreasing weights
GoArray.clear(_weightMap);
GoArray.clear(_colorMap);
for (int i=start; i<end; i++)
{
int moveXY = playoutMoves.get(i);
if (_colorMap[moveXY]==0)
{
_colorMap[moveXY] = color;
_weightMap[moveXY] = weight;
}
weight -= weightDelta;
color = opposite(color);
}
while (playoutNode!=null)
{
color =
opposite(playoutNode.getContent().getMove().getColor());
boolean playerWins = (blackWins && color==BLACK) || (!blackWins
&& color==WHITE);
double score = playerWins ?
MonteCarloTreeSearchResult.MAX_SCORE :
MonteCarloTreeSearchResult.MIN_SCORE;
for (int i=0;
i<playoutNode.getChildCount(); i++)
{
TreeNode<MonteCarloTreeSearchResult<MoveType>> nextNode =
playoutNode.getChildAt(i);
MonteCarloTreeSearchResult<MoveType> result =
nextNode.getContent();
GoMove move = (GoMove)
result.getMove();
int xy = move.getXY();
if (_colorMap[xy]==color)
result.increaseVirtualPlayouts(_weightMap[xy]*score,_weightMap[xy]);
}
playoutNode = playoutNode.getParent();
}
}
playoutNode is the move-node from which the playout was done. The amaf
values are stored in its children by the increaseVirtualPlayout()
method. Note that it goes up the tree by assigning the parent to
playoutNode until it gets to the root.
For more context it would be better to lookup the whole source at
http://plug-and-go.dev.java.net
If you think some more comments in the code could clarify things
better I'm open to suggestions.
Good luck.
Mark
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