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# wbetastat

## PURPOSE

Mean and variance for the Beta distribution.

## SYNOPSIS

[m,v]= wbetastat(a,c);

## DESCRIPTION

``` WBETASTAT Mean and variance for the Beta distribution.

CALL:  [m,v] = wbetastat(df1,df2)

m,  v = the mean and variance, respectively
a,  b = parameters of the Beta distribution

Mean (m) and variance (v) for the Beta distribution is

m = a/(a+b) and v = a*b/(a+b)^2/(a+b+1)  if a>0, b>0

## CROSS-REFERENCE INFORMATION

This function calls:
 comnsize Check if all input arguments are either scalar or of common size. error Display message and abort function. nan Not-a-Number. warning Display warning message; disable or enable warning messages.
This function is called by:

## SOURCE CODE

```001 function [m,v]= wbetastat(a,c);
002 %WBETASTAT Mean and variance for the Beta distribution.
003 %
004 % CALL:  [m,v] = wbetastat(df1,df2)
005 %
006 %   m,  v = the mean and variance, respectively
007 %   a,  b = parameters of the Beta distribution
008 %
009 %  Mean (m) and variance (v) for the Beta distribution is
010 %
011 %      m = a/(a+b) and v = a*b/(a+b)^2/(a+b+1)  if a>0, b>0
012 %
014
015
016 % Reference: Cohen & Whittle, (1988) "Parameter Estimation in Reliability
017 % and Life Span Models", Marcel Dekker.
018
019
020 % Tested on; Matlab 5.3
021 % History:
022 % by pab 23.10.2000
023
024 error(nargchk(2,2,nargin))
025 [errorcode, a, c] = comnsize(a,c);
026 if errorcode > 0
027     error('a and b must be of common size or scalar.');
028 end
029
030
031 %   Initialize Mean and Variance to zero.
032 m = zeros(size(a));
033 v = zeros(size(a));
034
035 ok = (a > 0  & c > 0 );
036 k = find(ok);
037 if any(k)
038   m(k) = a(k)./(a(k)+c(k));
039   v(k) = m(k).*c(k)./(a(k)+c(k))./(a(k)+c(k)+1);
040 end
041
042 k1 = find(~ok);
043 if any(k1)
044   warning('a and b should be positive')
045   tmp = NaN;
046   v(k1) = tmp(ones(size(k1)));
047   m(k) = v(k1);
048 end
049
050
051```

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

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