# Computer Chess Club Archives

## Messages

### Subject: Re: new thoughts on verified null move

Author: Alessandro Damiani

Date: 17:15:31 11/23/02

Go up one level in this thread

```On November 23, 2002 at 13:42:06, Omid David Tabibi wrote:

>On November 23, 2002 at 13:29:38, Martin Giepmans wrote:
>
>>On November 23, 2002 at 12:52:21, Omid David Tabibi wrote:
>>
>>>On November 23, 2002 at 11:37:25, Martin Giepmans wrote:
>>>
>>>>On November 23, 2002 at 08:48:36, Omid David Tabibi wrote:
>>>>
>>>>>On November 23, 2002 at 08:45:00, Uri Blass wrote:
>>>>>
>>>>>>On November 23, 2002 at 08:11:37, scott farrell wrote:
>>>>>>
>>>>>>>Just after other people's thoughts.
>>>>>>>
>>>>>>>I think Omid's work overlooked the adapative null move searching many of us do,
>>>>>>>ie. transitioning from r=3 to r=2.
>>>>>>>
>>>>>>>I think adaptive null move tries to GUESS where to use r=2 to reduce the errors
>>>>>>>that R=3 makes. I guess it depends on how often this GUESS is correct, the cost
>>>>>>>of the verification search, and how long it takes the adaptive searching to
>>>>>>>catch the error at the next ply.
>>>>>>>
>>>>>>>Has anyone looked at setting the verification search to reduced depth of 2
>>>>>>>(rather than 1)? obviously to reduce the cost of the verification search.
>>>>>>
>>>>>>Omid checked it but you also reduce the gain.
>>>>>>
>>>>>>I think that I will look for good rules when to do the verification search so
>>>>>>the cost will be significantly smaller but the gain is going to be the same in
>>>>>>at least 99% of the cases.
>>>>>>
>>>>>
>>>>>I'm currently working on other variations. The initial results are promising.
>>>>>
>>>>>>Uri
>>>>
>>>>I have done some tests with your method at greater depths.
>>>>25% compared to pure R=3.
>>>
>>>Of course verified R=3 will *always* construct a larger tree than standard R=3.
>>>However, starting from a certain depth, it will always construct a smaller tree
>>>than standard R=2.
>>>
>>>Take note, that while verified R=3 constructs a slightly larger tree than
>>>standard R=3, it has a superior tactical strength to even R=2 !
>>>
>>>
>>>>
>>>>(my engine uses a simple Q-search that shouldn't give problems here)
>>>>
>>>>So the question is if your expectation that the treesize of R=3 and vrfd R=3
>>>>converge at greater depths (> 11) really holds.
>>>>
>>>>Needs more testing, I think.
>>>>
>>>>Another point:
>>>>I would expect that vrfd R=3 becomes less safe at greater depths.
>>>>The subtrees in which you don't verify nullmove (after the verification) become
>>>>deeper and I see no reason - on logical grounds - why this shouldn't give safety
>>>>problems.
>>>>Even if R=3 and vrfd R=3 converge in terms of treesize, the safety (or rather
>>>>the lack of it) might also converge ...
>>>>
>>>
>>>None will converge.
>>
>>That is what you hope. And hope is a good thing, for sure :)
>>
>
>That's what I hope? No, actually I would be happier if the tree size of vrfd R=3
>and std R=3 would converge! But that is impossible, since verified R=3 has the
>
>
>>
>
>Look at Figure 4. The deeper you go, the larger becomes the difference between
>the tree size of vrfd R=3 and std R=2.
>
>
>>>However, the deeper you go, the smaller will be the difference in tree size,  and the greater the difference in tactical strength.
>>>
>>Again, how do you know?
>>
>
>The "backbone" of verified null move pruning is R=3. So it is natural that the
>deeper you go, the size of the tree will be closer to standard R=3 than to
>standard R=2 (again see Figure 4).
>

Or in other words, R=3 dominates the verification search.

Alessandro

>>Martin
>>>
>>>>In any case, thanks for sharing.
>>>>
>>>>Martin

```