first version of obidemerge, obijoin and a new filter for obicleandb but to be finnished

Former-commit-id: 8a1ed26e5548c30db75644c294d478ec4d753f19

pkg/obistats/tdist.go

@@ -0,0 +1,37 @@
+package obistats
+
+//
+// Dupplicated code from internal module available at :
+// https://github.com/golang-design/bench.git
+//
+
+import "math"
+
+// A TDist is a Student's t-distribution with V degrees of freedom.
+type TDist struct {
+	V float64
+}
+
+// PDF is the probability distribution function
+func (t TDist) PDF(x float64) float64 {
+	return math.Exp(lgamma((t.V+1)/2)-lgamma(t.V/2)) /
+		math.Sqrt(t.V*math.Pi) * math.Pow(1+(x*x)/t.V, -(t.V+1)/2)
+}
+
+// CDF is the cumulative distribution function
+func (t TDist) CDF(x float64) float64 {
+	if x == 0 {
+		return 0.5
+	} else if x > 0 {
+		return 1 - 0.5*mathBetaInc(t.V/(t.V+x*x), t.V/2, 0.5)
+	} else if x < 0 {
+		return 1 - t.CDF(-x)
+	} else {
+		return math.NaN()
+	}
+}
+
+// Bounds ...
+func (t TDist) Bounds() (float64, float64) {
+	return -4, 4
+}