Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/financial-0.4.0/rate.m b/octave_packages/financial-0.4.0/rate.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} {@var{r} =} rate (@var{n}, @var{p}, @var{v})
+## @deftypefnx {Function File} {@var{r} =} rate (@var{n}, @var{p}, @var{v}, @var{l})
+## @deftypefnx {Function File} {@var{r} =} rate (@var{n}, @var{p}, @var{v}, @var{l}, @var{method})
+## @deftypefnx {Function File} {@var{r} =} rate (@var{n}, @var{p}, @var{v}, @var{method})
+## Return the rate of return @var{r} on an investment of present value @var{v}
+## which pays @var{p} in @var{n} consecutive periods.
+##
+## 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 string 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.
+## @seealso{pv, pmt, nper, npv}
+## @end deftypefn
+
+function r = rate (n, p, v, l = 0, m = "e")
+
+  if (nargin < 3 || nargin > 5)
+    print_usage ();
+  elseif (!isnumeric (n) || !isscalar (n) || n <= 0)
+    error ("number of consecutive periods `n' must be a positive scalar");
+  elseif (!isnumeric (p) || !isscalar (p))
+    error ("second argument `p' must be a numeric scalar");
+  elseif (!isnumeric (v) || !isscalar (v))
+    error ("present value `v' must be a numeric scalar");
+
+  ## the following checks is to allow using default value for `l' while specifying `m'
+  elseif (nargin == 5)
+    if (!isnumeric (l) || !isscalar (l))
+      error ("value of additional lump-sum payment `l' must be numeric scalar");
+    elseif (!ischar (m))
+      error ("`method' must be a string")
+    endif
+  elseif (nargin == 4)
+    if (ischar (l))
+      m = l;
+      l = 0;   # default value for `l' again
+    elseif (!isnumeric (l) || !isscalar (l))
+      error ("fourth argument must either be a numeric scalar for lump-sum payment `l' or a string for `method'");
+    endif
+  endif
+
+  if (!any (strcmpi (l, {"e","b"})))
+    error ("`method' must either be `e' or `b")
+  endif
+
+  f = @(x) pv (x, n, p, l, m) - v;
+  r = fsolve (f, 0);
+
+endfunction