function P = chisquared_prob(X2,v)%CHISQUARED_PROB computes the chi-squared probability function.%   P = CHISQUARED_PROB( X2, v ) returns P(X2|v), the probability%   of observing a chi-squared value <= X2 with v degrees of freedom.%   This is the probability that the sum of squares of v unit-variance%   normally-distributed random variables is <= X2.%   X2 and v may be matrices of the same size size, or either %   may be a scalar.%   %   e.g., CHISQUARED_PROB(5.99,2) returns 0.9500, verifying the%   95% confidence bound for 2 degrees of freedom. This is also%   cross-checked in, e.g., Abramowitz & Stegun Table 26.8%%   See also CHISQUARED_TABLE%%Peter R. Shaw, WHOI% References: Press et al., Numerical Recipes, Cambridge, 1986;% Abramowitz & Stegun, Handbook of Mathematical Functions, Dover, 1972.% Peter R. Shaw, Woods Hole Oceanographic Institution% Woods Hole, MA 02543% (508) 457-2000 ext. 2473  pshaw@whoi.edu% March, 1990; fixed Oct 1992 for version 4% Computed using the Incomplete Gamma function,% as given by Press et al. (Recipes) eq. (6.2.17)% Following nonsense is necessary from Matlab version 3 -> version 4versn_str=version; eval(['versn=' versn_str(1) ';']);if versn<=3, %sigh P = gamma(v/2, X2/2);else P = gammainc(X2/2, v/2);end