chiinv

Function for evaluating the inverse chi-squared distribution function.

Note: This function is only available in version 4.1.1 of NCL. If your site is licensed for version 4.1, then you can get version 4.1.1 for free. To get version 4.1.1 of NCAR Graphics software, please contact your site representative. If you don't know who your site representative is, then send email to ncarginf@ucar.edu or call (303) 497-1201.

Synopsis

    function chiinv(
        p   : float,
        df  : float
    )

Arguments

p: The integral from 0 to X of the chi-square distribution. [0<p<1]
df: degrees of freedom of the chi-square distribution. (0, +infinity)

Description

Calculates the upper integration of the non-central chi-square distribution. This gives the same answers as IMSL's chiin function.

Example

begin
  p  = 0.99
  df = 2.
  x  = chiinv (p,df)
  print ("p="+p+"   df="+df+"   x="+x)

  df = 64.
  x  = chiinv (p,df)
  print ("p="+p+"   df="+df+"   x="+x)

end

The result is:

(0)     p=0.99   df=2    x= 9.21034
(0)     p=0.99   df=64   x=93.2169

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$Revision: 1.2 $ $Date: 1999/04/29 21:32:17 $