Depth dependant aspiration window delta

jcalovski · mcostalba · commit 36c381154bcf · 2014-03-14T19:47:41.000+01:00
Split delta value in aspiration window so that when
search depth is less than 24 a smaller delta value
is used. The idea is that the search is likely to
be more accurate at lower depths and so we can exclude
more possibilities, 25% to be exact.

Passed STC
LLR: 2.96 (-2.94, 2.94) [-1.50, 4.50]
Total: 20430 W: 3775 L: 3618 D: 13037

And LTC
LLR: 2.96 (-2.94, 2.94) [0.00, 6.00]
Total: 5032 W: 839 L: 715 D: 3478

Bench: 7451319
diff --git a/src/search.cpp b/src/search.cpp
@@ -327,7 +327,7 @@ namespace {
             // Reset aspiration window starting size
             if (depth >= 5)
             {
-                delta = Value(16);
+                delta = Value(depth > 23 ? 16 : 12);
                 alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);
                 beta  = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);
             }

Original file line number	Diff line number	Diff line change
`@@ -327,7 +327,7 @@ namespace {`
`327`	`327`	`// Reset aspiration window starting size`
`328`	`328`	`if (depth >= 5)`
`329`	`329`	`{`
`330`		`- delta = Value(16);`
	`330`	`+ delta = Value(depth > 23 ? 16 : 12);`
`331`	`331`	`alpha = std::max(RootMoves[PVIdx].prevScore - delta,-VALUE_INFINITE);`
`332`	`332`	`beta = std::min(RootMoves[PVIdx].prevScore + delta, VALUE_INFINITE);`
`333`	`333`	`}`