## Copyright (C) 1995, 1996, 1997 Kurt Hornik ## ## This program is free software; you can redistribute it and/or modify ## it under the terms of the GNU General Public License as published by ## the Free Software Foundation; either version 2, or (at your option) ## any later version. ## ## This program is distributed in the hope that it will be useful, but ## WITHOUT ANY WARRANTY; without even the implied warranty of ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU ## General Public License for more details. ## ## You should have received a copy of the GNU General Public License ## along with this file. If not, write to the Free Software Foundation, ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. ## usage: chisquare_inv (x, n) ## ## For each element of x, compute the quantile (the inverse of the CDF) ## at x of the chisquare distribution with n degrees of freedom. ## Author: TT <Teresa.Twaroch@ci.tuwien.ac.at> ## Description: Quantile function of the chi-square distribution function inv = chisquare_inv (x, n) if (nargin != 2) usage ("chisquare_inv (x, n)"); endif [retval, x, n] = common_size (x, n); if (retval > 0) error ("chisquare_inv: x and n must be of common size or scalar"); endif inv = gamma_inv (x, n / 2, 1 / 2); ## Allow only for (positive) integer n. k = find (n != round (n)); if any (k) fprintf (stderr, ... "WARNING: n should be positive integer\n"); [r, c] = size (x); inv = reshape (inv, 1, r * c); inv(k) = NaN * ones (1, length (k)); inv = reshape (inv, r, c); endif endfunction

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