[ncl-talk] stat_dispersion and standard deviation

[Dennis Shea]

====
6.3.0

http://www.ncl.ucar.edu/current_release.shtml
Under 'Bugs Fixed'

*stat_dispersion*
<http://www.ncl.ucar.edu/Document/Functions/Contributed/stat_dispersion.shtml>
- The second returned element returned was the sample variance and not the
sample standard deviation as is documented. In 6.3.0, the sample standard
deviation will be returned.

=====

%> ncl -V
6.3.0

  a = (/-20.46505, -4.795454, -1.454606,-2.677286, -1.868608, -0.4972475,
1.18715, -1.657706, -3.428875, -2.766053, -1.689298, -0.3371645, -0.640966,
-0.7326741/)

  opt = True
  opt at PrintStat = True
  stata = stat_dispersion(a, opt )


Copyright (C) 1995-2015 - All Rights Reserved
 University Corporation for Atmospheric Research
 NCAR Command Language Version 6.3.0          <====================
 The use of this software is governed by a License Agreement.
 See http://www.ncl.ucar.edu/ for more details.
(0)
(0)       ===> Robust Dispersion Statistics <===
(0)     [0]            Mean=-2.98742
(0)     [1]          StdDev=5.24311    <=====
(0)     [2]             Min=-20.465
(0)     [3]          LowDec=-20.465
[SNIP]



On Fri, Apr 24, 2015 at 2:25 PM, jbuzan <jbuzan at purdue.edu> wrote:

> I don’t know if this has been fixed in 6.3.0, but there was a change in
> stat_dispersion and the standard deviation is no longer calculated.  it is
> the variance.
>
> you can change:
> $NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl
> (I renamed the file)
>
> and commented out:
>      ; statx(1) = moment(1)             ; std. deviation
>
> and replaced with:
>       statx(1) = stddev(x)             ; std. deviation
>
>
> -Jonathan
>
>
>
> On Apr 24, 2015, at 4:20 PM, Rainer Luptowitz <rlupt001 at ucr.edu> wrote:
>
> Hi ncl-talk,
>
> Is the standard deviation computed in the "stats_dispersion" function
> actually a variance?
>
> I test this and it appears to be variance instead of stats_dispersion as
> seen in with sample "a" below.
>
>
> Variable: a
> Type: float
> Total Size: 56 bytes
>             14 values
> Number of Dimensions: 1
> Dimensions and sizes: [ncl_join | 14]    ; I had joined 8 files trends
> with "addfiles" function
> Coordinates:
> Number Of Attributes: 0
> (0) -20.46505
> (1) -4.795454
> (2) -1.454606
> (3) -2.677286
> (4) -1.868608
> (5) -0.4972475
> (6) 1.18715
> (7) -1.657706
> (8) -3.428875
> (9) -2.766053
> (10) -1.689298
> (11) -0.3371645
> (12) -0.640966
> (13) -0.7326741
>
> ; ncl code compare variance to standard deviation
>
> ; the above data was placed into an array named "a"
> a = (/-20.46505, -4.795454, -1.454606,-2.677286, -1.868608, -0.4972475,
> 1.18715, -1.657706, -3.428875, -2.766053, -1.689298, -0.3371645, -0.640966,
> -0.7326741/)
>
>
> ; Input
> Var_a = variance(a)  ; calc variance
> print(Var_a)
> StdDev_a = stddev(a) ; calc standard deviation
> print(StdDev_a)
> opt = True
> opt at PrintStat = True
> Stats_a = stat_dispersion(a,opt)
>
>
> ; Output
> ; from individually calculating Variance
> Variable: Var_a
> Type: float
> Total Size: 4 bytes
>             1 values
> Number of Dimensions: 1
> Dimensions and sizes: [1]
> Coordinates:
> (0) 27.49021
>
> ; from individually calculating Standard Deviation
> Variable: StdDev_a
> Type: float
> Total Size: 4 bytes
>             1 values
> Number of Dimensions: 1
> Dimensions and sizes: [1]
> Coordinates:
> (0) 5.243111
>
> ; from Stats_Dispersion function.
> (0)
> (0)   ===> Robust Dispersion Statistics <===
> (0) [0]            Mean=-2.98742
> (0) [1]          StdDev=27.4902    ; this appears to be variance since
> (0) [2]             Min=-20.4651
> (0) [3]          LowDec=-20.4651
> (0) [4]          LowOct=-20.4651
> (0) [5]          LowSex=-4.79545
> (0) [6]     LowQuartile=-3.42888
> (0) [7]          LowTri=-2.76605
> (0) [8]          Median=-1.6735
> (0) [9]         HighTri=-1.45461
> (0) [10]   HighQuartile=-0.732674
> (0) [11]        HighSex=-0.640966
> (0) [12]        HighOct=-0.497248
> (0) [13]        HighDec=-0.497248
> (0) [14]            Max=1.18715
> (0) [15]          Range=21.6522
> (0) [16]     Dispersion=0.787633
> (0) [17]    RMS Anomaly=5.05239
> (0) [18]      #   Total=14
> (0) [19]      #    Used=14
> (0) [20]      # Missing=0
> (0) [21]      % Missing=0
> (0) [22]     Lower 0.1%=9.96921e+36
> (0) [23]     Lower 1.0%=9.96921e+36
> (0) [24]     Lower 5.0%=9.96921e+36
> (0) [25]     Upper 5.0%=9.96921e+36
> (0) [26]     Upper 1.0%=9.96921e+36
> (0) [27]     Upper 0.1%=9.96921e+36
> (0) [28]       Skewness=-2.57898
> (0) [29]       Kurtosis=5.86411
>
>
> What do you think?
>
> Thank you for time and assistance,
>
> *Rainer Luptowitz*
> *Grad Student *
> *Dept Earth Sciences*
> *UC Riverside*
> *rlupt001 at ucr.edu* <rlupt001 at ucr.edu>
>
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