[Plan] Tuning

I've started some tuning with CLOP which is an excellent piece of software. Of course I'd want a software completely focused on chess engine tuning, i.e. choose parameters, choose opponents, and receive optimal parameters and expected gain. But this very much good enough.

First tuned the futility levels which resulted in a quite expected (but hard to guess) increase in value of the shallow nodes. From:

120, 120, 310, 310, 400

to

210, 230, 260, 260, 460

So basically a higher margin before skipping searching nodes close to the leaves (remember futility pruning checks how far behind you are in the search and if the arbitrary margin doesn't get you back on the plus side, simply do not keep searching). And a slightly lower margin in nodes further from the leaves, and then slightly higher again for the nodes 5 plies from the leaves.

Pretty much what I expected (I borrowed the previous values from Crafty and generally thought they were a bit optimistic).

The next thing I tuned was the king positioning table in the endgame, which looked like this:

-20 -15 -10 -10 -10 -10 -15 -20 
-15  -5   0   0   0   0  -5 -15 
-10   0   5   5   5   5   0 -10 
-10   0   5  10  10   5   0 -10 
-10   0   5  10  10   5   0 -10 
-10   0   5   5   5   5   0 -10 
-15  -5   0   0   0   0  -5 -15 
-20 -15 -10 -10 -10 -10 -15 -20 

Again this was just randomly chosen (in this case I think I simply went with gut-feeling to pick the numbers). And I always suspected them to be too low, that is not giving enough credit for having the king in the center in the endgames.

Tuning gave this:

-187 -157 -128 -128 -128 -128 -157 -187
-157  -99  -70  -70  -70  -70  -99 -157
-128  -70  -41  -41  -41  -41  -70 -128
-128  -70  -41  -12  -12  -41  -70 -128
-128  -70  -41  -12  -12  -41  -70 -128
-128  -70  -41  -41  -41  -41  -70 -128
-157  -99  -70  -70  -70  -70  -99 -157
-187 -157 -128 -128 -128 -128 -157 -187

So a whole bunch lower, bit suprising... But bigger differences between center and edges (two pawns difference). I did a quick test of this, and over 200 games it seems it's certainly better (about 60% win rate over the old values).

I have a feeling my evaluation is so badly tuned that I'll be seeing a lot of these quite extreme numbers, and I might have to pass through all the variables a few times until I get them all right.

But I love this tuning business (which I've done very little of in the passed). Simply pass in a few parameters, wait a couple hours, and out comes an improved engine. No effort whatsoever. Silly really. :)

Next thing up is mobility which I have no idea how valid it is at the moment. Currently I do something like count the available squares for a piece, and give twice the number in centipawns along with half the number of unsafe squares (protected by lesser valued pieces).

This gives a really arbitrary number which I have no idea how good it is. Will be really interesting what CLOP comes up with.