Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / financial-0.4.0 / npv.m

diff --git a/octave_packages/financial-0.4.0/npv.m b/octave_packages/financial-0.4.0/npv.m
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+## Copyright (C) 1995-2000, 2002, 2004-2007 Kurt Hornik <Kurt.Hornik@wu-wien.ac.at>
+##
+## 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; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} npv (@var{r}, @var{p}, @var{i})
+## Net present value of a series of payments.
+##
+## 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
+
+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