Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/financial-0.4.0/nper.m b/octave_packages/financial-0.4.0/nper.m
new file mode 100644 (file)
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+++ b/octave_packages/financial-0.4.0/nper.m
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+## Copyright (C) 1995-1998, 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} {} nper (@var{r}, @var{p}, @var{a}, @var{l}, @var{method})
+## Return the number of regular payments of @var{p} necessary to
+## amortize @var{a} loan of amount @var{a} and interest @var{r}.
+##
+## The optional argument @var{l} may be used to specify an additional
+## lump-sum payment of @var{l} made at the end of the amortization time.
+##
+## The optional argument @var{method} may be used to specify whether
+## payments are made at the end (@var{"e"}, default) or at the beginning
+## (@var{"b"}) of each period.
+##
+## Note that the rate @var{r} is specified as a fraction (i.e., 0.05,
+## not 5 percent).
+## @seealso{pv, pmt, rate, npv}
+## @end deftypefn
+
+function n = nper (r, p, a, l, m)
+
+  if (nargin < 3 || nargin > 5)
+    print_usage ();
+  endif
+
+  if (! (isscalar (r) && r > -1))
+    error ("nper: r must be a scalar > -1");
+  elseif (! isscalar (p))
+    error ("nper: p must be a scalar");
+  elseif (! isscalar (a))
+    error ("nper: a must be a scalar");
+  endif
+
+  if (nargin == 5)
+    if (! ischar (m))
+      error ("nper: `method' must be a string");
+    endif
+  elseif (nargin == 4)
+    if (ischar (l))
+      m = l;
+      l = 0;
+    else
+      m = "e";
+    endif
+  else
+    m = "e";
+    l = 0;
+  endif
+
+  if (strcmp (m, "b"))
+    p = p * (1 + r);
+  endif
+
+  q = (p - r * a) / (p - r * l);
+
+  if (q > 0)
+    n = - log (q) / log (1 + r);
+  else
+    n = Inf;
+  endif
+
+endfunction