--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/finance/irr.m	Fri Oct 23 05:44:01 1998 +0000
@@ -0,0 +1,56 @@
+## 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:  irr (p [, i])
+##
+## Computes the internal rate of return of a series of payments p from
+## an initial investment i, i.e., the solution of npv (r, p) = i. If the
+## second argument is omitted, i = 0 is used.
+##
+## See also:  npv;  pv, rate.
+  
+## Author:  KH <Kurt.Hornik@ci.tuwien.ac.at>
+## Description:  Internal rate of return of an investment
+
+function r = irr (p, i)
+  
+  if (nargin == 1)
+    i = 0;
+  elseif !(nargin == 2)
+    usage ("irr (p [, i])");
+  endif
+  
+  tmp = output_precision;
+  output_precision = 15;
+  if !(is_vector (p))
+    error ("irr:  p must be a vector");
+  else
+    p_string = type p;
+  endif
+
+  if !is_scalar (i)
+    error ("irr:  i must be a scalar");
+  endif
+  
+  string = ["function delta = f (r) ", ...
+      "delta = npv (r, %s) - %g;  end"];
+  eval (sprintf (string, p_string, i));
+
+  r = fsolve ("f", 0.01);
+  
+  output_precision = tmp;
+  
+endfunction