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geometric_rnd.m

## 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:  geometric_rnd (p [, r, c])
##
## geometric_rnd (p) returns a matrix of random samples from the
## geometric distribution with parameter p.  The size of the matrix is
## the size of p.
##
## geometric_rnd (p, r, c) returns an r by c matrix of random samples
## from the geometric distribution with parameter p, which must be a
## scalar or of size r by c.
  
## Author:  KH <Kurt.Hornik@ci.tuwien.ac.at>
## Description:  Random deviates from the geometric distribution
  
function rnd = geometric_rnd (p, r, c)

  if (nargin == 3)
    if ( !(is_scalar (r) && (r > 0) && (r == round (r))) )
      error ("geometric_rnd:  r must be a positive integer");
    endif
    if ( !(is_scalar (c) && (c > 0) && (c == round (c))) )
      error ("geometric_rnd:  c must be a positive integer");
    endif
    [retval, p] = common_size (p, zeros (r, c));
    if (retval > 0)
      error (strcat("geometric_rnd:  ",
                "p must be scalar or of size ",
                sprintf ("%d by %d", r, c)));
    endif
  elseif (nargin != 1)
    usage ("geometric_rnd (p [, r, c])");
  endif
  
  [r, c] = size (p);
  s = r * c;
  p = reshape (p, 1, s);
  rnd = zeros (1, s);
  
  k = find (!(p >= 0) | !(p <= 1));
  if (any (k))
    rnd(k) = NaN * ones (1, length (k));
  endif
  
  k = find (p == 0);
  if (any (k))
    rnd(k) = Inf * ones (1, length (k));
  endif
  
  k = find ((p > 0) & (p < 1));
  if (any (k))
    rnd(k) = floor (log (rand (1, length (k))) ./ log (1 - p(k)));
  endif
  
  rnd = reshape (rnd, r, c);
  
endfunction

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