OK, thanks for the explanation, this makes it completely clear.Daniel Shawul wrote:There are winning captures ,as predicted by SEE, which are really loosing
but I dont see why identifying this cases is important.(other than statistics).
However, I still I don't think that because in 40% of the cases in hindsight the IID turned out not to be necessary for move selection, you can or should draw the conclusion that it is not useful. I pay health insurance, and in 60% of the years I don't need any medicare whatsoever. Is that a reason to drop the insurance? Would I have been better off not having the insurance all those years? You can never conclude that. Even if in 9 out of 10 years I would not have needed any medical attention, but in the one year I did I was hospitalized for open-heart surgery, it still saved my a million bucks... Especially if I get most of my insurance premium back through a 'no-claim' arrangement in the years that nothing happened.
To judge the value of an insurance, you should look at the disasters that you prevent, which of necessity are infrequent but very costly. (Otherwise it would make no sense to take an insurance, you will just ride the odds and let the statistical 'law of large numbers' do its job.) This should be weighted against the certain cost of the premium. That the premium is wasted if nothing happens is understood.
IID is an insurance against engaging in a very deep search that could have been avoided, because the SEE was not abslutely reliable and you search a bad move before the one that gave the cutoff. The bad move doesn't do anything for your alpha, so you still have to spend an equal amount of search the move that does cause the beta cutoff. A pilot search 2 plies less deep would perhaps have cost only 1% of the superfluous search, and would intercept virtually all mis-predictions by the SEE. So even if in 90% of the cases the pilot search was 'wasted' because the SEE was correct, you have invested 10 times 1% to gain back 1 times 100%, i.e. the total search effort in this node on the average reduces from 11 full-depth searches (9 times the refutation move straight away, 1 time as the second) to 10.1 (10 times the refutation move straight away, but also 10 times a pilot search costing 0.01). So you save ~8%, despite the fact that 90% of the IID searches was 'wasted'.
In the same way, IID would be insurance against the event that you would mistakenly judge the node as an alpha node, while a good non-obvious (i.e. non-SEE-able) move is available that makes it a beta or PV node. The pilot searches in IID can be ridiculously cheap compared to a full-depth search, since even in a very rudimentary form (say 1-ply + QS only) they are likely to be far more reliable than a SEE. If the full remaining depth is at 6, such a pilot is nearly free. So the SEE- or node-type judgement must really be enormously reliable (say error rate les than 0,01%) before you lose on taking the IID insurance.
