Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/financial-0.4.0/pv.m b/octave_packages/financial-0.4.0/pv.m
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+## Copyright (C) 1995-1996, 1998, 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} {} pv (@var{r}, @var{n}, @var{p}, @var{l}, @var{method})
+## Returns the present value of an investment that will pay off @var{p} for @var{n}
+## consecutive periods, assuming an interest @var{r}.
+##
+## The optional argument @var{l} may be used to specify an additional
+## lump-sum payment made at the end of @var{n} periods.
+##
+## The optional argument @var{method} may be used to specify whether
+## payments are made at the end (@code{"e"}, default) or at the
+## beginning (@code{"b"}) of each period.
+##
+## Note that the rate @var{r} is specified as a fraction (i.e., 0.05,
+## not 5 percent).
+## @seealso{pmt, nper, rate, npv}
+## @end deftypefn
+
+function v = pv (r, n, p, l, m)
+
+  if (nargin < 3 || nargin > 5)
+    print_usage ();
+  endif
+
+  if (! (isscalar (r) && r > -1))
+    error ("pv: r must be a scalar > -1");
+  elseif (! (isscalar (n) && n > 0))
+    error ("pv: n must be a positive scalar");
+  elseif (! isscalar (p))
+    error ("pv: p must be a scalar");
+  endif
+
+  if (r != 0)
+    v = p * (1 - (1 + r)^(-n)) / r;
+  else
+    v = p * n;
+  endif
+
+  if (nargin > 3)
+    if (nargin == 5)
+      if (! ischar (m))
+        error ("pv: `method' must be a string");
+      endif
+    elseif (ischar (l))
+      m = l;
+      l = 0;
+    else
+      m = "e";
+    endif
+    if (strcmp (m, "b"))
+      v = v * (1 + r);
+    endif
+    if (isscalar (l))
+      v = v + pvl (r, n, l);
+    else
+      error ("pv: l must be a scalar");
+    endif
+  endif
+
+endfunction