## Copyright (C) 1995, 1996, 1997  Friedrich Leisch
##
## 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.

## -*- texinfo -*-
## @deftypefn {Function File} {} wiener_rnd (@var{t}, @var{d}, @var{n})
## Return a simulated realization of the @var{d}-dimensional Wiener Process
## on the interval [0,@var{t}].  If @var{d} is omitted, @var{d} = 1 is
## used. The first column of the return matrix contains time, the
## remaining columns contain the Wiener process.
##
## The optional parameter @var{n} gives the number of summands used for
## simulating the process over an interval of length 1.  If @var{n} is
## omitted, @var{n} = 1000 is used.
## @end deftypefn

## Author: FL <Friedrich.Leisch@ci.tuwien.ac.at>
## Description: Simulate a Wiener process

function retval = wiener_rnd (t, d, n)

  if (nargin == 1)
    d = 1;
    n = 1000;
  elseif (nargin == 2)
    n = 1000;
  elseif (nargin > 3)
    usage ("wiener_rnd (t, d,n)");
  endif

  retval = randn (n * t, d);
  retval = cumsum (retval) / sqrt (n);

  retval = [((1: n*t)' / n), retval];

endfunction