function p = chi2cdf(x,v)
%CHI2CDF Chi-square cumulative distribution function.
%   P = CHI2CDF(X,V) returns the chi-square cumulative distribution
%   function with V degrees of freedom at the values in X.
%   Subtract this value from 1.0 to get the significance probability.

if   nargin < 2, 
    error('Requires two input arguments.');
end

[errorcode x v] = distchck(2,x,v);

if errorcode > 0
    error('Requires non-scalar arguments to match in size.');
end
    
% Call the gamma distribution function. 
p = gamcdf(x,v/2,2);

% Return NaN if the degrees of freedom is not a positive integer.
k = find(v < 0  |  round(v) ~= v);
if any(k)
   tmp = NaN;
    p(k) = tmp(ones(size(k)));
end