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### Subject: Re: Question for the MTD(f) experts

Author: Dann Corbit

Date: 10:58:58 04/14/04

Go up one level in this thread

On April 14, 2004 at 13:51:17, Bo Persson wrote:
>On April 14, 2004 at 04:57:01, Dann Corbit wrote:
>
>
>>Picking out the hash value and moving the lookup to the end gives a bit better
>>result:
>>
>>/* MTD(f) is an alternative search to pvs */
>>int mtdf(int f, int depth)
>>{
>> int beta;
>> int smallest = -INFINITY;
>> int greatest = INFINITY;
>> TranspositionEntry *entry;
>>
>> do {
>> if (f == smallest)
>> beta = f + 1;
>> else
>> beta = f; /* beta is starting with a first best guess */
>> f = AlphaBeta(beta - 1, beta, depth);
>
>You have a problem right here, if you don't use fail-soft. The returned value
>will always be either beta or beta-1.
>
>
>> if (f < beta)
>> greatest = f;
>> else {
>> int j;
>> smallest = f; /* performs a cut-off */
>
>Say you got beta-1 from AlphaBeta. Then you set greatest = beta-1, and try again
>with a window one single point lower. How long does it take to reach down to the
>the real upper bound?
It depends on how good your initial guess was. I have a database with hundreds
of millions of analyzed positions, so I figured MTD(f) was a very natural
approach, since I will often have a very good estimate.
I was playing around and trying to understand the algorithm better.

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