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I just downloaded the latest free version of Komodo 12 to try to disable the Null Move Pruning option. So, in my mind, I supposed that for depth 2, it will need 20*20= 400 nodes However I arrived at depth 3 with nodes 78 and depth 4 with 193.

What is the role of the Null Move Pruning option? I thought that it would search every single position even if the moves were disastrous.

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  • Null Move Pruning is only one of many pruning methods used, so after disabling it there will still be other methods that are active. That being said even without any "unsafe" pruning you still wouldn't have 400 nodes for depth 2 thanks to the alpha beta algorithm. Also note that depth these days is a rather vague term, it doesn't mean that most lines if any lines are of that depth. – koedem Feb 25 at 10:37
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The theory is that if your opponent could make two consecutive moves and not improve his position, you must have an overwhelming advantage. If you advantage is so great, there's no need to examine other lines, and the search can end.

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  • Thanks for the answer, but is there a way to throw away every prunning with an other engine or different options? – Ropdup Feb 24 at 16:26
  • @Ropdup Stockfish being open source should make it possible if nothing else to disable it in the code directly. You might want to ask in the Stockfish discord. Not sure it is easily possible with Komodo. – koedem Feb 25 at 10:35
  • The Komodo 12 page gives the procedure that you already tried, so either the command line is broken or there's the engine is giving the wrong output. Maybe the engine does some sort of IDD, where it would reach ply 4 before it completed the search at a lower ply, therefore giving a lower perft. Any source code, like Stockfish and Crafty, would allow you to edit any function, but even experienced programmers try this alternative and fail. A hex edit option would solve any problem would be too much a waste of time to even attempt. – Mike Jones Mar 1 at 0:34

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