; NAME: 
;      SDEV
; 
; VERSION: 1
; 
; PURPOSE: 
;      Return the mean and standard deviation of a sample of numbers
; 
; CALLING SEQUENCE: 
;      answer = sdev(numbers, [prnt=prnt, help=help])
; 
; INPUTS: 
;      numbers- An array of numbers
; 
; OPTIONAL KEYWORD INPUTS: 
;      prnt- Set to print result to screen
;      help- Set to nonzero scalar to have SDEV print syntax 
; 
; OUTPUT: 
;      answer- two element floating point vector with mean and s.d.
; 
; EXTERNAL CALLS: 
;      NONE 
; 
; COMMON BLOCKS: 
;      NONE 
; 
; MODIFICATION HISTORY: 
;      - Written by Eric Volquardsen, NASA IRTF, Feb. 2003
; 
; =======================================================================
FUNCTION sdev, numbers, answer, prnt=prnt, help=help

; CHECK INPUTS
   IF n_elements(help) EQ 1 THEN BEGIN
        IF help NE 0 THEN help = 1 
   ENDIF ELSE help = 0 
   IF n_elements(numbers) LT 2 THEN help = 1 
   IF help EQ 1 THEN BEGIN
        print, '*********************************************'
        print, '***              SDEV SYNTAX              ***' 
        print, '*** > answer = sdev(numbers, print=print) ***' 
        print, '***                                       ***' 
        print, '*** numbers- array of numbers             ***' 
        print, '*** print- set to print results           ***' 
        print, '*********************************************'
        RETURN, 0 
   ENDIF 
   numbers = float(numbers)
   IF n_elements(prnt) NE 1 THEN prnt = 0 
   IF prnt NE 0 THEN prnt = 1 

; CALCULATE MEAN
   n = float(n_elements(numbers)) 
   mn = total(numbers)/n

; CALCULATE STANDARD DEVIATION
   stp1 = (numbers - mn)^2
   stp2 = (total(stp1))/(n-1)
   sd = sqrt(stp2)

; GIVE ANSWER
   answer = [mn, sd]
   mn = strtrim(string(mn), 2)
   sd = strtrim(string(sd), 2)
   IF prnt EQ 1 THEN BEGIN
        print, 'mean = ', mn
        print, 'standard deviation = ', sd
   ENDIF

   RETURN, answer

END