Mercurial > octave-nkf
view scripts/finance/nper.m @ 3407:5e0a0b1cba43
[project @ 2000-01-06 03:13:55 by jwe]
author | jwe |
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date | Thu, 06 Jan 2000 03:14:17 +0000 |
parents | e4f4b2d26ee9 |
children | ae7adbb591e8 |
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## Copyright (C) 1995, 1996, 1997 Kurt Hornik ## ## 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 2, 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 file. If not, write to the Free Software Foundation, ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. ## -*- texinfo -*- ## @deftypefn {Function File} {} nper (@var{r}, @var{p}, @var{a} [, @var{l}] [, @var{method}]) ## ## Computes the number of regular payments of @var{p} necessary to amortize @var{a} ## loan of amount @var{a} and interest @var{r}. ## ## With the optional scalar argument @var{l}, one can specify an additional ## lump-sum payment of @var{l} made at the end of the amortization time. With ## the optional string argument `method', one can specify whether ## payments are made at the end ("e", default) or at the beginning ("b") ## of each period. ## ## Note that the rate r is not specified in percent, i.e., one has to ## write 0.05 rather than 5 %. ## @end deftypefn ## @seealso{pv, pmt, rate, npv} ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> ## Description: Number of payments needed for amortizing a loan function n = nper (r, p, a, l, m) if ((nargin < 3) || (nargin > 5)) usage ("nper (r, p, a [, l] [, method])"); endif if !(is_scalar (r) && (r > -1)) error ("nper: r must be a scalar > -1"); elseif !is_scalar (p) error ("nper: p must be a scalar"); elseif !is_scalar (a) error ("nper: a must be a scalar"); endif if (nargin == 5) if !isstr (m) error ("nper: `method' must be a string"); endif elseif (nargin == 4) if isstr (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