// SelectArm returns 1 indexed arm to be tried next.
func (u *uCB1) SelectArm() int {
for i, count := range u.counts {
if count == 0 {
u.counts[i]++
return i + 1
}
}
var totalCounts int
for _, count := range u.counts {
totalCounts += count
}
ucbValues := make([]float64, u.arms)
for i := 0; i < u.arms; i++ {
bonus := math.Sqrt((2 * math.Log(float64(totalCounts))) / float64(u.counts[i]))
ucbValues[i] = u.values[i] + bonus
}
_, imax := bmath.Max(ucbValues)
// best arm. randomly pick because there may be equally best arms.
arm := imax[u.rand.Intn(len(imax))]
u.counts[arm]++
return arm + 1
}
// SelectArm returns 1 indexed arm to be tried next.
func (s *softmax) SelectArm() int {
max, _ := bmath.Max(s.values)
normalizer := 0.0
for _, value := range s.values {
normalizer += math.Exp((value - max) / s.tau)
}
if math.IsInf(normalizer, 0) {
panic("normalizer in softmax too large")
}
cumulativeProb := 0.0
draw := len(s.values) - 1
z := s.rand.Float64()
for i, value := range s.values {
cumulativeProb = cumulativeProb + math.Exp((value-max)/s.tau)/normalizer
if cumulativeProb > z {
draw = i
break
}
}
s.counts[draw]++
return draw + 1
}
// SelectArm returns 1 indexed arm to be tried next.
func (e *epsilonGreedy) SelectArm() int {
arm := 0
if z := e.rand.Float64(); z > e.epsilon {
_, imax := bmath.Max(e.values)
// best arm. randomly pick because there may be equally best arms.
arm = imax[e.rand.Intn(len(imax))]
} else {
// random arm
arm = e.rand.Intn(e.arms)
}
e.counts[arm]++
return arm + 1
}
// SelectArm returns 1 indexed arm to be tried next.
func (t *thompson) SelectArm() int {
var thetas = make([]float64, t.arms)
for i := 0; i < t.arms; i++ {
si := t.values[i] * float64(t.counts[i])
fi := float64(t.counts[i]) - si
thetas[i] = t.betaRand.NextBeta(si+t.alpha, fi+t.alpha)
}
_, imax := bmath.Max(thetas)
// best arm. randomly pick because there may be equally best arms.
arm := imax[t.rand.Intn(len(imax))]
t.counts[arm]++
return arm + 1
}
