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+++ b/scripts/statistics/distributions/chisquare_rnd.m
@@ -0,0 +1,66 @@
+## 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_rnd (n [, r, c])
+##
+## chisquare_rnd (n) returns a matrix of random samples from the
+## chisquare distribution with n degrees of freedom.  The size of the
+## matrix is the size of n.
+##
+## chisquare_rnd (n, r, c) returns an r by c matrix of random samples
+## from the chisquare distribution with n degrees of freedom.  n must be
+## a scalar or of size r by c.
+  
+## Author:  KH <Kurt.Hornik@ci.tuwien.ac.at>
+## Description:  Random deviates from the chi-square distribution
+
+function rnd = chisquare_rnd (n, r, c)
+
+  if (nargin == 3)
+    if ( !(is_scalar (r) && (r > 0) && (r == round (r))) )
+      error ("chisquare_rnd:  r must be a positive integer");
+    endif
+    if ( !(is_scalar (c) && (c > 0) && (c == round (c))) )
+      error ("chisquare_rnd:  c must be a positive integer");
+    endif
+    [retval, n] = common_size (n, zeros (r, c));
+    if (retval > 0)
+      error (strcat("chisquare_rnd:  ",
+		    "n must be scalar or of size ",
+		    sprintf ("%d by %d", r, c)));
+    endif
+  elseif (nargin != 1)
+    usage ("chisquare_rnd (n [, r, c])");
+  endif
+  
+  [r, c] = size (n);
+  s = r * c;
+  n = reshape (n, 1, s);
+  rnd = zeros (1, s);
+  
+  k = find (!(n > 0) | !(n < Inf) | !(n == round (n)));
+  if (any (k))
+    rnd(k) = NaN * ones (1, length (k));
+  endif
+  
+  k = find ((n > 0) & (n < Inf) & (n == round (n)));
+  if (any (k))
+    rnd(k) = chisquare_inv (rand (1, length (k)), n(k));
+  endif
+  
+  rnd = reshape (rnd, r, c);
+  
+endfunction