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wfpdf

PURPOSE ^

Snedecor's F probability density function

SYNOPSIS ^

f = wfpdf(x,a,b)

DESCRIPTION ^

 WFPDF Snedecor's F probability density function
 
  CALL:  f = wfpdf(x,df1,df2);
 
        f = PDF evaluated at x
        x = matrix
  df1,df2 = degrees of freedom (1,2,....)
  
  Example:
    x  = linspace(0,6,200);
    p1 = wfpdf(x,1,1); p2 = wfpdf(x,2,2);
    plot(x,p1,x,p2)

CROSS-REFERENCE INFORMATION ^

This function calls: This function is called by:

SOURCE CODE ^

001 function f = wfpdf(x,a,b)
002 %WFPDF Snedecor's F probability density function
003 %
004 % CALL:  f = wfpdf(x,df1,df2);
005 %
006 %       f = PDF evaluated at x
007 %       x = matrix
008 % df1,df2 = degrees of freedom (1,2,....)
009 % 
010 % Example:
011 %   x  = linspace(0,6,200);
012 %   p1 = wfpdf(x,1,1); p2 = wfpdf(x,2,2);
013 %   plot(x,p1,x,p2)
014 
015 % tested on matlab 5.3
016 %History:
017 %revised pab 29.10.2000
018 % adapted from stixbox
019 % -added nargchk, comnsize + a check that df1,df2 are positive integers
020 %        Anders Holtsberg, 18-11-93
021 %        Copyright (c) Anders Holtsberg
022 
023 
024 error(nargchk(3,3,nargin))
025 [errorcode x,a,b] = comnsize(x,a,b);
026 if errorcode>0,
027   error('x, df1 and df2 must be of common size or scalar');
028 end
029 
030 f = zeros(size(x));
031 
032 ok = (a>0 & b>0 & floor(a)==a & floor(b)==b);
033 
034 k = find(x>=0 & ok);
035 if any(k)
036   c = b(k)./a(k);
037   xx = x(k)./(x(k)+c(k));
038   tmp = wbetapdf(xx,a(k)/2,b(k)/2);
039   f(k) = tmp./(x(k)+c(k)).^2.*c(k);
040 end
041 
042 
043 k3=find(~ok);
044 if any(k3)
045   tmp=NaN;
046   xf(k3)=tmp(ones(size(k3)));
047 end
048 
049 
050 
051 
052 
053 
054 
055

Mathematical Statistics
Centre for Mathematical Sciences
Lund University with Lund Institute of Technology

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