update vendor/

vendor/github.com/crillab/gophersat/solver/lbd.go

@@ -0,0 +1,89 @@
+package solver
+
+const (
+	nbMaxRecent      = 50 // How many recent LBD values we consider; "X" in papers about LBD.
+	triggerRestartK  = 0.8
+	nbMaxTrail       = 5000 // How many elements in queueTrail we consider; "Y" in papers about LBD.
+	postponeRestartT = 1.4
+)
+
+type queueData struct {
+	totalNb   int     // Current total nb of values considered
+	totalSum  int     // Sum of all values so far
+	nbRecent  int     // NB of values used in the array
+	ptr       int     // current index of oldest value in the array
+	recentAvg float64 // Average value
+}
+
+// lbdStats is a structure dealing with recent LBD evolutions.
+type lbdStats struct {
+	lbdData      queueData
+	trailData    queueData
+	recentVals   [nbMaxRecent]int // Last LBD values
+	recentTrails [nbMaxTrail]int  // Last trail lengths
+}
+
+// mustRestart is true iff recent LBDs are much smaller on average than average of all LBDs.
+func (l *lbdStats) mustRestart() bool {
+	if l.lbdData.nbRecent < nbMaxRecent {
+		return false
+	}
+	return l.lbdData.recentAvg*triggerRestartK > float64(l.lbdData.totalSum)/float64(l.lbdData.totalNb)
+}
+
+// addConflict adds information about a conflict that just happened.
+func (l *lbdStats) addConflict(trailSz int) {
+	td := &l.trailData
+	td.totalNb++
+	td.totalSum += trailSz
+	if td.nbRecent < nbMaxTrail {
+		l.recentTrails[td.nbRecent] = trailSz
+		old := float64(td.nbRecent)
+		new := old + 1
+		td.recentAvg = (td.recentAvg*old)/new + float64(trailSz)/new
+		td.nbRecent++
+	} else {
+		old := l.recentTrails[td.ptr]
+		l.recentTrails[td.ptr] = trailSz
+		td.ptr++
+		if td.ptr == nbMaxTrail {
+			td.ptr = 0
+		}
+		td.recentAvg = td.recentAvg - float64(old)/nbMaxTrail + float64(trailSz)/nbMaxTrail
+	}
+	if td.nbRecent == nbMaxTrail && l.lbdData.nbRecent == nbMaxRecent && trailSz > int(postponeRestartT*td.recentAvg) {
+		// Too many good assignments: postpone restart
+		l.clear()
+	}
+
+}
+
+// addLbd adds information about a recent learned clause's LBD.
+// TODO: this is very close to addConflicts's code, this should probably be rewritten/merged.
+func (l *lbdStats) addLbd(lbd int) {
+	ld := &l.lbdData
+	ld.totalNb++
+	ld.totalSum += lbd
+	if ld.nbRecent < nbMaxRecent {
+		l.recentVals[ld.nbRecent] = lbd
+		old := float64(ld.nbRecent)
+		new := old + 1
+		ld.recentAvg = (ld.recentAvg*old)/new + float64(lbd)/new
+		ld.nbRecent++
+	} else {
+		old := l.recentVals[ld.ptr]
+		l.recentVals[ld.ptr] = lbd
+		ld.ptr++
+		if ld.ptr == nbMaxRecent {
+			ld.ptr = 0
+		}
+		ld.recentAvg = ld.recentAvg - float64(old)/nbMaxRecent + float64(lbd)/nbMaxRecent
+	}
+}
+
+// clear clears last values. It should be called after a restart.
+func (l *lbdStats) clear() {
+	l.lbdData.ptr = 0
+	l.lbdData.nbRecent = 0
+	l.lbdData.recentAvg = 0.0
+}