func StdDevP(input Float64Data) (sdev float64, err error) {
	return StandardDeviationPopulation(input)
}
StdDevP is a shortcut to StandardDeviationPopulation
package stats
func VarP(input Float64Data) (sdev float64, err error) {
	return PopulationVariance(input)
}
func VarS(input Float64Data) (sdev float64, err error) {
	return SampleVariance(input)
}