Author: Peter Fendrich
Date: 04:25:09 03/24/04
Go up one level in this thread
On March 24, 2004 at 05:39:20, Tord Romstad wrote:
>On March 24, 2004 at 05:17:56, Peter Fendrich wrote:
>
>>Uri didn't invent ETC if that's what you imply!
>>
>>Given your story about costly move/unmove functions it's possible that ETC gives
>>you some savings. Without ETC you will hit the cutoff anyway in the child node
>>and with smaller unmove costs ETC is not that effective IMHO.
>
>It seems to me that you miss part of the idea of ETC. You are right that
>you will get the cutoff in the child node even without ETC, but in which
>child node? If your move ordering is not perfect, there is a risk that
>you will have to search many moves before you get the cutoff. When you
>use ETC, you check the hash values for *all* child nodes before you
>start searching, which can sometimes save a lot of nodes.
>
>To me, ETC has always been a clear win. The last time I made any
>experiments, it reduced my tree size by about 10% at high search depths.
>I am fairly sure it is a technique which works better with MTD(f) than
>with more conventional search algorithms, though.
>
>Tord
Well, not really. We have different programs but you're right I forgot to
mention the move ordering part.
I don't sort moves at all. I generate them in stages and play them before the
next stage is generated. The stages are hashmove, good captures and so on...
In the last stage (if no cutoff was produced before) I generate all of the
remaining moves and pick the 3-5 (depending on prev. history) "best" moves in
order but without sorting. After that I just take the moves in the order they
occur in the list.
This is what I've tested with ETC:
- In the stage picking the 3-5 moves I go through the moves
and probe the hashtab using the hashkey they would produce.
- If a child FH is found handle it and take the next move.
- If a child FL is found the current node is finished.
- If the probe announce a hash hit inside the A/B window,
assign that value to the move and act accordingly
(in some cases finish the current node)
- Otherwise go on as before
I haven't seen any win at all even if the tree shrinks. On the contrary it is a
loser for me...
/Peter
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