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Introduce voting system for best move selection

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Introduce voting system for best move selction in multi-threads mode.
Joint work with Stefan Geschwentner, based on ideas introduced by
Michael Stembera.

Moves are upvoted by every thread using the margin to the minimum score
across threads and the completed depth.

First thread voting for the winner move is selected as best thread.

Passed STC, LTC. A further LTC test with only 4 threads failed with positive
score. A LTC with 31 threads was stopped with LLR 0.77 after 25k games to
avoid use of excessive resources (equivalent to 1.5M STC games).

Similar ideas were proposed by Michael Stembera 2 years ago #507, #508.
This implementation seems simpler and more understandable, the results
slightly more promising.

Further possible work:

1) Tweak of the formula using for assigning votes.
2) Use a different baseline for the score dependent part: maximum score
or winning probability could make more sense.
3) Assign votes in `Thread::Search` as iterations are completed and use
voting results to stop search.
4) Select best thread as the threads voting for best move with the highest
completed depth or, alternatively, vote on PV moves.

Link to SPRT tests

[stopped LTC, 31 threads 20+0.02](http://tests.stockfishchess.org/tests/view/5b61dc090ebc5902bdb95192)
LLR: 0.77 (-2.94,2.94) [0.00,5.00]
Total: 25602 W: 3977 L: 3850 D: 17775
Elo: 1.70 [-0.68,4.07] (95%)

[passed LTC, 8 threads 20+0.02](http://tests.stockfishchess.org/tests/view/5b5df5180ebc5902bdb9162d)
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 44478 W: 7602 L: 7300 D: 29576
Elo: 1.92 [-0.29,3.94] (95%)

[failed LTC, 4 threads 20+0.02](http://tests.stockfishchess.org/tests/view/5b5f39ef0ebc5902bdb92792)
LLR: -2.94 (-2.94,2.94) [0.00,5.00]
Total: 29922 W: 5286 L: 5285 D: 19351
Elo: 0.48 [-1.98,3.10] (95%)

[passed STC, 4 threads 5+0.05](http://tests.stockfishchess.org/tests/view/5b5dbf0f0ebc5902bdb9131c)
LLR: 2.97 (-2.94,2.94) [0.00,5.00]
Total: 9108 W: 2033 L: 1858 D: 5217
Elo: 6.11 [1.26,10.89] (95%)

No functional change (in simple threat mode)
This commit is contained in:
Stefano Cardanobile 2018-07-04 21:54:38 +02:00 • committed by Stéphane Nicolet
parent 571f54b176
commit d96c1c32a2
1 changed files with 20 additions and 8 deletions
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28
src/search.cpp
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@ -246,18 +246,30 @@ void MainThread::search() {
&& !Skill(Options["Skill Level"]).enabled()
&& rootMoves[0].pv[0] != MOVE_NONE)
{
for (Thread* th : Threads)
{
Depth depthDiff = th->completedDepth - bestThread->completedDepth;
Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
std::map<Move, int> votes;
Value minScore = this->rootMoves[0].score;
// Select the thread with the best score, always if it is a mate
if ( scoreDiff > 0
&& (depthDiff >= 0 || th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY))
bestThread = th;
// Find out minimum score and reset votes for moves which can be voted
for (Thread* th: Threads){
minScore = std::min(minScore, th->rootMoves[0].score);
votes[th->rootMoves[0].pv[0]] = 0;
}
// Vote according to score and depth
for (Thread* th : Threads)
votes[th->rootMoves[0].pv[0]] += int(th->rootMoves[0].score - minScore) + int(th->completedDepth);
// Select best thread
int bestVote = votes[this->rootMoves[0].pv[0]];
for (Thread* th : Threads){
if (votes[th->rootMoves[0].pv[0]] > bestVote){
bestVote = votes[th->rootMoves[0].pv[0]];
bestThread = th;
}
}
}
previousScore = bestThread->rootMoves[0].score;
// Send again PV info if we have a new best thread