An alternative to IID

[hgm]

Good chance that this would makes them weaker. This looks a lot like "Unmotivated Reduction of Everything" (UROE), because hash moves can be lost by any number of reasons. If this is also done in all-nodes, virtually all all-nodes would be reduced, as these typically do not have a hash move in a stable search.

Reducing everything but the PV isn't necessarily bad. Even reducing everything including the PV would not be detrimental, it just means you lie more about your depth. If reducing everything but the PV gives an improvement, it means your normal reduction scheme wasn't tuned well. Under those conditions random extra reductions outside the PV can also give an improvement.

[Rebel]

Good chance that this would makes them weaker. This looks a lot like "Unmotivated Reduction of Everything" (UROE), because hash moves can be lost by any number of reasons. If this is also done in all-nodes, virtually all all-nodes would be reduced, as these typically do not have a hash move in a stable search.

Reducing everything but the PV isn't necessarily bad. Even reducing everything including the PV would not be detrimental, it just means you lie more about your depth. If reducing everything but the PV gives an improvement, it means your normal reduction scheme wasn't tuned well. Under those conditions random extra reductions outside the PV can also give an improvement.

What if I tell you that at longer time control (CCRL Blitz) it gives even more elo, currently +35.

And it's not "Unmotivated", it's a another (but different) way (like IID) to handle large unsorted subtrees.

[Rebel]

Internal Iterative Deepening (IID) becomes :

Internal Iterative Reductions (IIR)

or TTR

Nice! IIR, I like it.

I wonder what it would do in one of the super strong, 3000 ELO+ engines?

That I worry too, see the OP.

For the moment I notice a considerable lower branch factor which automatically leads to 1 or 2 more iterations and formerly reduced nodes due to the lack of a hash move become alive because now that there is a hash move. The worry is that IIR may become counter productive when the TT is saturated, so depending on the size of the TT (or the % filled) there has to be a depth limit.

[RubiChess]

I can confirm that replacing IID with this idea gives +12 Elo in my engine.
Credits will go to Ed in the merge and the ChangeLog

[hgm]

And it's not "Unmotivated", it's a another (but different) way (like IID) to handle large unsorted subtrees.

IID is motivated by the desire to reduce the search time of a deep tree by first obtaining some info to sort on in a comparatively cheap way. But eventually you would still search the intended tree, it doesn't change what you search in any way.

That a tree is unsorted, or merely had its hash move overwritten, doesn't seem to be a valid motivation for reducing its search depth. Unless you would consider it a valid motivation to do reductions based on the day of the week, or when the TickCount is odd...

Considering the positive test results I am sure absence of a hash move must strongly correlate with some more fundamental property of the node. Like I said, perhaps this means you are doing it in every all-node. But in that case it should even work better if you just did it in every all-node, and nowhere else, irrespective of whether there was a hash move or not.

[RubiChess]

I can confirm that replacing IID with this idea gives +12 Elo in my engine.
Credits will go to Ed in the merge and the ChangeLog

Oh shit. Seems that I mixed two patches and now I need to find out which one is the Elo gainer...
Stay tuned.

[RubiChess]

I can confirm that replacing IID with this idea gives +12 Elo in my engine.
Credits will go to Ed in the merge and the ChangeLog

Oh shit. Seems that I mixed two patches and now I need to find out which one is the Elo gainer...
Stay tuned.

Sorry. Seems it was the other patch that won the Elo. Replacing IID with the "decrease depth" idea is < 1 Elo.

[silentshark]

Took IID out (of my oldie) and replaced it with a full ply reduction without research and it gave me +17 elo after 5000 games.

Not sure if that works for modern searchers.

Interesting idea. I will give this a go, as I've never been happy with my IID implementation anyway. Will post back results after a few thousand games.

+13 ELO after 2.5K games for me.. looking interesting

+14 ELO after 7.5K games for me now..

This does spark other ideas. I might try the following - tweaking LMR reduction, e.g reduce more if there is not a hash move

Anyhow, Ed's idea seems to have promise on its own. Overall depth increases quite a lot (like 1 or 2 plies), and strength increases slightly.

Seems to be holding at about +14 ELO after 14K games for me. These games are 60 moves in 1 minute, vs earlier version of my engine, and vs some other sparring partners.

[Rebel]

I can confirm that replacing IID with this idea gives +12 Elo in my engine.
Credits will go to Ed in the merge and the ChangeLog

Oh shit. Seems that I mixed two patches and now I need to find out which one is the Elo gainer...
Stay tuned.

Sorry. Seems it was the other patch that won the Elo. Replacing IID with the "decrease depth" idea is < 1 Elo.

I am not surprised, engines like yours already search at incredible depths.

In the old days IID was a winner, I looked at SF and it says about IID ~1 elo.

[Terje]

Replacing IID with this gains 3-8 elo in Weiss, lower with higher TC / threadcount.