public double stDev ( double [ ] series ) { double num0 = 0D ; double sum = 0D ; int count = 0 ; for ( double tp : series ) { num0 = num0 + tp * tp ; sum = sum + tp ; count += 1 ; } double len = ( ( Integer ) count ) . doubleValue ( ) ; return Math . sqrt ( ( len * num0 - sum * sum ) / ( len * ( len - 1 ) ) ) ; }
Speed - optimized implementation .