Standard deviation of particular location and of area

[Charles Seman]

Raj,

here's some documentation from a script used to calculate standard
deviation:

*  From statistics (reference: "Statistical Concepts and Methods"
*  by Bhattacharyya and Johnson (1977)), the sample variance s**2
*  for a set of "N" observations of a variable "xi" (x1,...,xN)
*  is defined as:
*
*    s**2 = [(x1-xbar)**2 + (x2-xbar)**2 + (x3-xbar)**2 +....
*          + (xN-xbar)**2 ]/(N-1) ,  (from page 34)
*
*  where the sample mean = xbar = (x1+x2+x3+...+xN)/N , (from page 27)
*
*  Note, the sample variance sums over "N" observations, and divides the
*  sum by "N-1"...
*
*  The sample standard deviation is defined as the square root of the
*  sample variance (from page 35):
*
*    s = sqrt(s**2)

perhaps you could try (please check for mistakes)
...same as in your email, then
sg = 0
tt = it
while(tt<='et')
'set t 'tt
...define whu at t = "tt"
sg = sg + pow((avg-whu),2)
endwhile
dt = et-it+1
sv = sg/(dt-1)   * sample variance
'd sqrt(sv)'
std = subwrd(result,4)
say 'STD DEV = ',std

Hope this helps,
Chuck

Raj Kumar Sharma wrote:
> Hi, I have file containing global values of variable for whole year. I
> would like to compute Average & Standard Deviation for Particular
> Location and also for defined area.
> I had written script to compute Std Dev for a particular location,
> however it is showing error. It will be great if someone can help.
>
> Raj
>
> 'reinit'
> 'set display color white'
> clear
> 'set gxout shaded'
> 'open pqfull.ctl'
> ln = 60
> lt = -10
> it = 1
> et = 5
>
> 'set lon 'ln
> 'set lat 'lt
>
> 'd ave(whu,t='it',t='et')'
> lin=sublin(result,2)
> avg = subwrd(lin,4)
> say 'AAAA 'avg
> while(t<'et')
> sg = sg + (avg-whu)
> df =  pow(sg,2)
> endwhile
> dt = et-it+1
> std = df/dt
> 'd sqrt(std)'
> std = subwrd(result,4)
> say 'STD DEV = ',std
> return
>
>
> Dr Raj Kumar
>
>
> <http://sigads.rediff.com/RealMedia/ads/click_nx.ads/www.rediffmail.com/signatureline.htm@Middle?>

--

Please note that Charles.Seman at noaa.gov should be considered my NOAA
email address, not cjs at gfdl.noaa.gov.

********************************************************************
 Charles Seman                                Charles.Seman at noaa.gov
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 Geophysical Fluid Dynamics Laboratory         voice: (609) 452-6547
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