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## 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: weibull_rnd (alpha, sigma [, r, c])
##
## weibull_rnd (alpha, sigma) returns a matrix of random samples from
## the Weibull distribution with parameters alpha and sigma. The size of
## the matrix is the common size of alpha and sigma.
##
## weibull_rnd (alpha, sigma, r, c) returns an r by c matrix of random
## samples from the Weibull distribution with parameters alpha and sigma
## which must be scalar or of size r by c.
## Author: KH <Kurt.Hornik@ci.tuwien.ac.at>
## Description: Random deviates from the Weibull distribution
function rnd = weibull_rnd (shape, scale, r, c)
if (nargin == 4)
if ( !(is_scalar (r) && (r > 0) && (r == round (r))) )
error ("weibull_rnd: r must be a positive integer");
endif
if ( !(is_scalar (c) && (c > 0) && (c == round (c))) )
error ("weibull_rnd: c must be a positive integer");
endif
[retval, shape, scale] = common_size (shape, scale, zeros (r, c));
if (retval > 0)
error (strcat("weibull_rnd: ",
"alpha and sigma must be scalar or of size ",
sprintf ("%d by %d", r, c)));
endif
elseif (nargin == 2)
[retval, shape, scale] = common_size (shape, scale);
if (retval > 0)
error (strcat("weibull_rnd: ",
"alpha and sigma must be of common size or scalar"));
endif
else
usage ("weibull_rnd (alpha, sigma [, r, c])");
endif
[r, c] = size (shape);
s = r * c;
shape = reshape (shape, 1, s);
scale = reshape (scale, 1, s);
rnd = NaN * ones (1, s);
k = find ((shape > 0) & (shape < Inf) & (scale > 0) & (scale < Inf));
if any (k)
rnd(k) = (scale(k)
.* (- log (1 - rand (1, length (k)))) .^ (1 ./ shape(k)));
endif
rnd = reshape (rnd, r, c);
endfunction
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