[Refactor] Change standard-deviation calculation API slightly

2 files changed, 10 insertions, 5 deletions

diff --git a/ms/ms.go b/ms/ms.go
index fc0fe95..76b4b0a 100644
--- a/ms/ms.go
+++ b/ms/ms.go
@@ -80,7 +80,7 @@ func (ma *MathematicalSeries[T]) AllSequentialIncreasesLessThan(limit float64) (
 /*
  * N.B.: Overflow is possible -- use at your discretion!
  */
-func (ma *MathematicalSeries[T]) StandardDeviationLessThan(limit T) (bool, T) {
+func (ma *MathematicalSeries[T]) StandardDeviation() (bool, T) {
 
 	// If we have not yet accumulated a complete set of intervals,
 	// we are always false.
@@ -117,11 +117,16 @@ func (ma *MathematicalSeries[T]) StandardDeviationLessThan(limit T) (bool, T) {
 	sd := T(math.Sqrt(variance))
 	//sd := T(variance)
 
-	return T(sd) < limit, sd
+	return true, sd
 }
 
 func (ma *MathematicalSeries[T]) IsNormallyDistributed() bool {
-	_, stddev := ma.StandardDeviationLessThan(0.0)
+	valid, stddev := ma.StandardDeviation()
+	// If there are not enough values in our series to generate a standard
+	// deviation, then we cannot do this calculation either.
+	if !valid {
+		return false
+	}
 	avg := float64(ma.CalculateAverage())
 
 	fstddev := float64(stddev)
diff --git a/ms/ms_test.go b/ms/ms_test.go
index 86a5488..6f1e807 100644
--- a/ms/ms_test.go
+++ b/ms/ms_test.go
@@ -67,7 +67,7 @@ func Test_SequentialIncreasesAlwaysLessThanWithWraparoundInverse(test *testing.T
 	}
 }
 
-func Test_StandardDeviationLessThan_Float(test *testing.T) {
+func Test_StandardDeviationCalculation(test *testing.T) {
 	series := NewMathematicalSeries[float64](5)
 	// 5.7, 1.0, 8.6, 7.4, 2.2
 	series.AddElement(5.7)
@@ -76,7 +76,7 @@ func Test_StandardDeviationLessThan_Float(test *testing.T) {
 	series.AddElement(7.4)
 	series.AddElement(2.2)
 
-	if islt, sd := series.StandardDeviationLessThan(2.94); !islt {
+	if _, sd := series.StandardDeviation(); !utilities.ApproximatelyEqual(2.93, sd, 0.01) {
 		test.Fatalf("Standard deviation max calculation failed: %v.", sd)
 	} else {
 		test.Logf("Standard deviation calculation result: %v", sd)