func (s *Summary) StdDev() float64 {
	return math.Sqrt(s.Variance)
}
StdDev returns the standard deviation of the sample.
package tinystat
import (
	"math"
	"gonum.org/v1/gonum/stat"
	"gonum.org/v1/gonum/stat/distuv"
)
type Summary struct {
	N        float64  
	Mean     float64  
	Variance float64  
}