/*
KullbackLeiblerDivergence comput and return the divergence of two string based
on their character probabability.
*/
func KullbackLeiblerDivergence(a, b string) (divergence float64) {
aCharsd, aValuesd := tekstus.CountAlnumDistribution(a)
bCharsd, bValuesd := tekstus.CountAlnumDistribution(b)
sumValuesA := numerus.IntsSum(aValuesd)
sumValuesB := numerus.IntsSum(bValuesd)
charsDiff := tekstus.RunesDiff(aCharsd, bCharsd)
aMin, _, _ := numerus.IntsFindMin(aValuesd)
bMin, _, _ := numerus.IntsFindMin(bValuesd)
min := aMin
if bMin < aMin {
min = bMin
}
epsilon := float64(min) * 0.001
gamma := 1.0 - (float64(len(charsDiff)) * epsilon)
// Check if sum of a up to 1.
var sum float64
for _, v := range aValuesd {
sum += float64(v) / float64(sumValuesA)
}
sumDiff := 1 - math.Abs(sum)
if sumDiff > 0.000009 {
return 0
}
sum = 0
for _, v := range bValuesd {
sum += float64(v) / float64(sumValuesB)
}
sumDiff = 1 - math.Abs(sum)
if sumDiff > 0.000009 {
return 0
}
for x, v := range aCharsd {
probA := float64(aValuesd[x]) / float64(sumValuesA)
probB := epsilon
contain, atIdx := tekstus.RunesContain(bCharsd, v)
if contain {
probB = gamma * (float64(bValuesd[atIdx]) /
float64(sumValuesB))
}
divergence += (probA - probB) * math.Log(probA/probB)
}
return divergence
}
func doRunesDiff(t *testing.T, l, r, exp []rune) {
got := tekstus.RunesDiff(l, r)
assert(t, string(exp), string(got), true)
}