/usr/share/octave/packages/financial-0.4.0/irr.m is in octave-financial 0.4.0-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | ## 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} {} irr (@var{p}, @var{i})
## Return the internal rate of return of a series of payments @var{p}
## from an initial investment @var{i} (i.e., the solution of
## @code{npv (r, p) = i}. If the second argument is omitted, a value of
## 0 is used.
## @seealso{npv, pv, rate}
## @end deftypefn
function r = irr (p, i = 0)
## Check input
if (nargin != 1 && nargin != 2)
print_usage ();
elseif (! (isvector (p)))
error ("irr: p must be a vector");
elseif (! isscalar (i))
error ("irr: i must be a scalar");
endif
## Solve system
f = @(x) npv (x, p) - i;
r = fsolve (f, 0);
endfunction
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