Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/financial-0.4.0/pmt.m b/octave_packages/financial-0.4.0/pmt.m
new file mode 100644 (file)
index 0000000..9b662c1
--- /dev/null
+++ b/octave_packages/financial-0.4.0/pmt.m
@@ -0,0 +1,66 @@
+## 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} {} pmt (@var{r}, @var{n}, @var{a}, @var{l}, @var{method})
+## Return the amount of periodic payment necessary to amortize a loan
+## of amount a with interest rate @var{r} in @var{n} periods.
+##
+## The optional argument @var{l} may be used to specify a terminal
+## lump-sum payment.
+##
+## 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.
+## @seealso{pv, nper, rate}
+## @end deftypefn
+
+function p = pmt (r, n, a, l, m)
+
+  if (nargin < 3 || nargin > 5)
+    print_usage ();
+  endif
+
+  if (! (isscalar (r) && r > -1))
+    error ("pmt: rate must be a scalar > -1");
+  elseif (! (isscalar (n) && n > 0))
+    error ("pmt: n must be a positive scalar");
+  elseif (! (isscalar (a) && a > 0))
+    error ("pmt: a must be a positive scalar");
+  endif
+
+  if (nargin == 5)
+    if (! ischar (m))
+      error ("pmt: `method' must be a string");
+    endif
+  elseif (nargin == 4)
+    if (ischar (l))
+      m = l;
+      l = 0;
+    else
+      m = "e";
+    endif
+  else
+    l = 0;
+    m = "e";
+  endif
+
+  p = r * (a - l * (1 + r)^(-n)) / (1 - (1 + r)^(-n));
+
+  if (strcmp (m, "b"))
+    p = p / (1 + r);
+  endif
+
+endfunction