## 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.

## usage:  pvl (r, n, p)
##
## Returns the present value of an investment that will pay off p in one
## lump sum at the end of n periods, given the interest rate r.

## Author:  KH <Kurt.Hornik@ci.tuwien.ac.at>
## Description:  Present value of an investment that pays off at the end

function v = pvl (r, n, p)
  
  if (nargin != 3)
    usage ("pvl (r, n, p)");
  endif
  
  if !(is_scalar (r) && (r > -1))
    error ("pvl:  r has to be a scalar > -1");
  elseif !(is_scalar (n) && (n > 0))
    error ("pvl:  n has to be a positive scalar");
  elseif !is_scalar (p)
    error ("pvl:  p has to be a scalar");
  endif
  
  v = p / (1 + r)^n;
  
endfunction