;$Id: variance.pro,v 1.9 2004/01/21 15:55:04 scottm Exp $ ; ; Copyright (c) 1997-2004, Research Systems, Inc. All rights reserved. ; Unauthorized reproduction prohibited. ;+ ; NAME: ; VARIANCE ; ; PURPOSE: ; This function computes the statistical variance of an ; N-element vector. ; ; CATEGORY: ; Statistics. ; ; CALLING SEQUENCE: ; Result = variance(X) ; ; INPUTS: ; X: An N-element vector of type integer, float or double. ; ; KEYWORD PARAMETERS: ; DOUBLE: IF set to a non-zero value, computations are done in ; double precision arithmetic. ; ; NAN: If set, treat NaN data as missing. ; ; EXAMPLE: ; Define the N-element vector of sample data. ; x = [65, 63, 67, 64, 68, 62, 70, 66, 68, 67, 69, 71, 66, 65, 70] ; Compute the mean. ; result = variance(x) ; The result should be: ; 7.06667 ; ; PROCEDURE: ; VARIANCE calls the IDL function MOMENT. ; ; REFERENCE: ; APPLIED STATISTICS (third edition) ; J. Neter, W. Wasserman, G.A. Whitmore ; ISBN 0-205-10328-6 ; ; MODIFICATION HISTORY: ; Written by: GSL, RSI, August 1997 ;- FUNCTION variance, X, Double = Double, NaN = NaN ON_ERROR, 2 RETURN, (moment( X, Double=Double, Maxmoment=2, NaN = NaN ))[1] END