/usr/share/octave/packages/financial-0.4.0/nper.m is in octave-financial 0.4.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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##
## 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} {} nper (@var{r}, @var{p}, @var{a}, @var{l}, @var{method})
## Return the number of regular payments of @var{p} necessary to
## amortize @var{a} loan of amount @var{a} and interest @var{r}.
##
## The optional argument @var{l} may be used to specify an additional
## lump-sum payment of @var{l} made at the end of the amortization time.
##
## The optional argument @var{method} may be used to specify whether
## payments are made at the end (@var{"e"}, default) or at the beginning
## (@var{"b"}) of each period.
##
## Note that the rate @var{r} is specified as a fraction (i.e., 0.05,
## not 5 percent).
## @seealso{pv, pmt, rate, npv}
## @end deftypefn
function n = nper (r, p, a, l, m)
if (nargin < 3 || nargin > 5)
print_usage ();
endif
if (! (isscalar (r) && r > -1))
error ("nper: r must be a scalar > -1");
elseif (! isscalar (p))
error ("nper: p must be a scalar");
elseif (! isscalar (a))
error ("nper: a must be a scalar");
endif
if (nargin == 5)
if (! ischar (m))
error ("nper: `method' must be a string");
endif
elseif (nargin == 4)
if (ischar (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
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