/usr/share/octave/packages/interval-1.4.1/@infsupdec/pownrev.m is in octave-interval 1.4.1-1.
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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 -*-
## @documentencoding UTF-8
## @deftypemethod {@@infsupdec} {@var{X} =} pownrev (@var{C}, @var{X}, @var{P})
## @deftypemethodx {@@infsupdec} {@var{X} =} pownrev (@var{C}, @var{P})
##
## Compute the reverse monomial @code{x^@var{P}}.
##
## That is, an enclosure of all @code{x ∈ @var{X}} where
## @code{pown (x, @var{P}) ∈ @var{C}}.
##
## Accuracy: The result is a valid enclosure. The result is a tight
## enclosure for @var{P} ≥ -2. The result also is a tight enclosure if the
## reciprocal of @var{P} can be computed exactly in double-precision.
##
## @comment DO NOT SYNCHRONIZE DOCUMENTATION STRING
## No one way of decorating this operations gives useful information in all
## contexts. Therefore, the result will carry a @code{trv} decoration at best.
##
## @seealso{@@infsupdec/pown}
## @end deftypemethod
## Author: Oliver Heimlich
## Keywords: interval
## Created: 2014-10-13
function result = pownrev (c, x, p)
if (nargin < 2 || nargin > 3)
print_usage ();
return
endif
if (nargin < 3)
p = x;
x = infsupdec (-inf, inf);
endif
if (not (isa (c, "infsupdec")))
c = infsupdec (c);
endif
if (not (isa (x, "infsupdec")))
x = infsupdec (x);
endif
if (isnai (c))
result = c;
return
endif
if (isnai (x))
result = x;
return
endif
result = infsupdec (pownrev (intervalpart (c), intervalpart (x), p), "trv");
endfunction
%!assert (isequal (pownrev (infsupdec (25, 36), infsupdec (0, inf), 2), infsupdec (5, 6, "trv")));
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