## Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2002, 2004, 2005, ## 2006, 2007 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 3 of the License, 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 program; see the file COPYING. If not, see ## <http://www.gnu.org/licenses/>. ## -*- texinfo -*- ## @deftypefn {Function File} {} npv (@var{r}, @var{p}, @var{i}) ## Returns the net present value of a series of irregular (i.e., not ## necessarily identical) payments @var{p} which occur at the ends of @var{n} ## consecutive periods. @var{r} specifies the one-period interest rates and ## can either be a scalar (constant rates) or a vector of the same ## length as @var{p}. ## ## The optional argument @var{i} may be used to specify an initial ## investment. ## ## Note that the rate @var{r} is specified as a fraction (i.e., 0.05, ## not 5 percent). ## @seealso{irr, pv} ## @end deftypefn ## Author: KH <Kurt.Hornik@wu-wien.ac.at> ## Description: Net present value of a series of payments function v = npv (r, p, i) if (nargin < 2 || nargin > 3) print_usage (); endif if (! (isvector (p))) error ("npv: p has to be a vector"); else n = length (p); p = reshape (p, 1, n); endif if (any (any (r <= -1))) error ("npv: all interest rates must be > -1"); endif if (isscalar (r)) d = 1 ./ (1 + r) .^ (0 : n); elseif (isvector (r) && (length (r) == n)) d = [1, (1 ./ cumprod (reshape (1 + r, 1, n)))]; else error ("npv: r must be a scalar or a vector of the same length as p"); endif if (nargin == 3) if (! isscalar (i)) error ("npv: I_0 must be a scalar"); endif else i = 0; endif p = [i, p]; v = sum (d .* p); endfunction

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