pro prob_ks, D, N_eff, probks
;+
; NAME:
; PROB_KS
; PURPOSE:
; Return the significance of the Kolmogoroff-Smirnov statistic
; EXPLANATION:
; Returns the significance level of an observed value of the
; Kolmogorov-Smirnov statistic D for an effective number of data points
; N_eff. Called by KSONE and KSTWO
;
; CALLING SEQUENCE:
; prob_ks, D, N_eff, probks
;
; INPUT PARAMATERS:
; D - Kolmogorov statistic, floating scalar, always non-negative
; N_eff - Effective number of data points, scalar. For a 2 sided test
; this is given by (N1*N2)/(N1+N2) where N1 and N2 are the number
; of points in each data set.
;
; OUTPUT PARAMETERS:
; probks - floating scalar between 0 and 1 giving the significance level of
; the K-S statistic. Small values of PROB suggest that the
; distribution being tested are not the same
;
; REVISION HISTORY:
; Written W. Landsman August, 1992
; Corrected typo (termbv for termbf) H. Ebeling/W.Landsman March 1996
; Probably did not affect numeric result, but iteration went longer
; than necessary
; Converted to IDL V5.0 W. Landsman September 1997
;-
On_error,2
if N_params() LT 3 then begin
print,'Syntax - prob_ks, D, N_eff, prob'
print,' D - Komolgorov-Smirnov statistic, input'
print,' N_eff - effective number of data points, input'
print,' prob - Significance level of D, output'
return
endif
eps1 = 0.001 ;Stop if current term less than EPS1 times previous term
eps2 = 1.e-8 ;Stop if current term changes output by factor less than EPS2
en = sqrt( N_eff )
lambda = (en + 0.12 + 0.11/en)*D
a2 = -2.*lambda^2
probks = 0.
termbf = 0.
sign = 1.
for j = 1,100 do begin
term = sign*2*exp(a2*j^2)
probks = probks + term
if ( abs(term) LE eps1*termbf ) or $
( abs(term) LE eps2*probks ) then return
sign = -sign ;Series alternates in sign
termbf = abs(term)
endfor
probks = 1. ;Sum did not converge after 100 iterations
return
end