func StandardDeviationSample(input Float64Data) (sdev float64, err error) {
	if input.Len() == 0 {
		return math.NaN(), EmptyInput
	}
	vs, _ := SampleVariance(input)
	return math.Pow(vs, 0.5), nil
}
StandardDeviationSample finds the amount of variation from a sample
package stats
import "math"
func MedianAbsoluteDeviation(input Float64Data) (mad float64, err error) {
	return MedianAbsoluteDeviationPopulation(input)
}
func MedianAbsoluteDeviationPopulation(input Float64Data) (mad float64, err error) {
	if input.Len() == 0 {
		return math.NaN(), EmptyInput
	}
	i := copyslice(input)
	m, _ := Median(i)
	for key, value := range i {
		i[key] = math.Abs(value - m)
	}
	return Median(i)
}
func StandardDeviation(input Float64Data) (sdev float64, err error) {
	return StandardDeviationPopulation(input)
}
func StandardDeviationPopulation(input Float64Data) (sdev float64, err error) {
	if input.Len() == 0 {
		return math.NaN(), EmptyInput
	}
	vp, _ := PopulationVariance(input)
	return math.Pow(vp, 0.5), nil
}