Two things: Firstly, I'm storing (only in RAM) the precalculated Winrate and
InvSqrtVisits and keeping them updated.
So my UCT formula went from
Wins / Visits + sqrt(lnParentVisits / Visits)
to
WinRate + sqrtLnParentVisits * InvSqrtVisits;
This has a memory cost, but I don't care so much about RAM since I can send the
nodes to disk.
And the second thing is to store in the parent node a reference to what is likely the UCT-best child node. If the parent has been visited 100*boardspaces
times, I will go directly to the likely-best child with probability 2047/2048. Anytime a proper UCT loop occurs, the likely-best reference is updated (about
90% of the time there is no change, so I think it's safe).
Jason House wrote:
That sounds like a good optimization. What did you do?
Sent from my iPhone
On Jun 2, 2009, at 3:16 PM, Michael Williams
<michaelwilliam...@gmail.com> wrote:
Update: After concentrating on tightening the UCT loop, I've
optimized myself back into needing the SDD :/
But now I should be able to get to 20B nodes in just one day.
(still only doing 7x7 Go)
Michael Williams wrote:
Yes, when memory is full, I save and free all leaf nodes (which is
the vast majority). Nodes are loaded as needed.
Don Dailey wrote:
On Mon, Jun 1, 2009 at 4:57 PM, Michael Williams
<michaelwilliam...@gmail.com <mailto:michaelwilliam...@gmail.com>>
wrote:
I've optimized my disk access to the point where I'm mostly CPU
limited now, even when using a standard hard disk instead of an SSD.
I can now create trees of up to about 30 billion nodes, which would
take about a week. The simulation rate is continuously going down
because so much time is spent in UCT loops in the huge tree.
That's impressive. Are you doing things which move parts of the
tree onto the disk and back when needed? I'm curious about the
details!
- Don
Don Dailey wrote:
On Mon, Jun 1, 2009 at 11:22 AM, Isaac Deutsch <i...@gmx.ch
<mailto:i...@gmx.ch> <mailto:i...@gmx.ch <mailto:i...@gmx.ch>>>
wrote:
> Well, I'll take that over crashing with an out-of-memory
error. :)
Still, pruning seems better to me and has the same effect. ;p
But is it better? I think it's not so obvious without thorough
testing.
Pruning throw away information that is lost forever and may need
to be recalculated. Requiring more simulations does not throw
out results, but results in some inefficiencies. So it's not
clear to me which is better - it may even be that it depends on
how much you push it. I am just guessing but I would guess
that pruning is better in the short term, worse in the longer
term. Imagine a search at a corespondence level, where the
computer thinks for 24 hours. Which method is best
there? Could you use hard disk or SSD? Using some kind of
caching
system, where you relegate the oldest unvisited nodes to the
hard dirve. It may be that nodes you might normally prune are
unlikely to get used again but if they do you still have the
data. This is no good unless you can guarantee that the disk
is used very infrequently - but with SSD it may be more
practical.
- Don
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