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genNormalDist

Generates a normal distribution.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl" ; This library is automatically loaded
 ; from NCL V6.2.0 onward.
 ; No need for user to explicitly load.
	function genNormalDist (
		xAve [1] : numeric, 
		xStd [1] : numeric, 
		opt [1] : logical 
	)
	return_val [*] : float or double

Arguments

xAve

A scalar specifying the mean of the distribution.

xStd

A scalar specifying the standard deviation of the distribution.

opt

Attributes may be associated with this variable. The attributes will alter the default behavior of the genNormalDist.

Setting opt=False will result in default values being used.
Setting opt=True will activate use of the options.

spn - Change the span of the generated distribution. The default is 3.0 standard deviations. This means that 99.7% of all values will fall within this range.
npts - The number of points to be generated. The default is 101. It is not necessary that an odd number be used. Using an odd number results in a return array that will contain the central value. NOTE: Beginning with 6.2.0, the attribute N will be a synonym for npts

Return value

A one-dimensional array of size=101 or, if the N attribute is set to size=N. The following attributes will be associated with the return variable.

x - the generated abscissa values.

Description

Uses the standard formula:

 normal(xAve,xStd) = [1/(xStd*sqrt(2*pi)]*exp[-(0.5*(x-xAve)^2/xStd^2)

where

 spn = 3.0 ; default is 3.0 standard deviations
 x = fspan( (xAve-spn*xStd), (xAve+spn*xStd), N)

Examples

Example 1

Using default settings:

 nd = genNormalDist(100,10, False) 
 print(sprintf("%5.2f", nd@x)+" "+sprintf("%9.6f", nd)+" "+sprintf("%9.6f", nd@xsd) )

The print(...) yields:

 Variable: nd
 Type: float
 Total Size: 404 bytes
 101 values
 Number of Dimensions: 1
 Dimensions and sizes:	[101]
 Coordinates: 
 Number Of Attributes: 3
 long_name :	Normal Distribution
 x :	ARRAY of 101 elements
 xsd :	ARRAY of 101 elements
 nd@x nd nd@xsd 
(0) 70.00 0.000443 -3.000000
(1) 70.60 0.000530 -2.940000
(2) 71.20 0.000631 -2.880000
(3) 71.80 0.000748 -2.820000
(4) 72.40 0.000885 -2.760000
(5) 73.00 0.001042 -2.700000
[snip]
(47) 98.20 0.039253 -0.180000
(48) 98.80 0.039608 -0.120000
(49) 99.40 0.039822 -0.060000
(50) 100.00 0.039894 0.000000
(51) 100.60 0.039822 0.060000
(52) 101.20 0.039608 0.120000
(53) 101.80 0.039253 0.180000
[snip]
(95) 127.00 0.001042 2.700000
(96) 127.60 0.000885 2.760001
(97) 128.20 0.000748 2.820000
(98) 128.80 0.000631 2.880000
(99) 129.40 0.000530 2.939999
(100) 130.00 0.000443 3.000000

A simple x-y plot could be generated by using the returned x attribute values as the abscissa values and the "nd" values as ordinate values.

 wks = gsn_open_wks ("x11","PDFX")
 res = True
 res@gsnCenterString = "default 101 values"
 plot = gsn_csm_xy (wks, nd@x, nd, res)

Example 2:

Specify that 51 values be generated. The default is to generate 101 values.