/usr/share/octave/packages/interval-1.4.1/@infsup/log.m is in octave-interval 1.4.1-1.
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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 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 | ## Copyright 2014-2016 Oliver Heimlich
##
## 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
## @defmethod {@@infsup} log (@var{X})
##
## Compute the natural logarithm.
##
## The function is only defined where @var{X} is positive.
##
## Accuracy: The result is a tight enclosure.
##
## @example
## @group
## log (infsup (2))
## @result{} ans ⊂ [0.69314, 0.69315]
## @end group
## @end example
## @seealso{@@infsup/exp, @@infsup/log2, @@infsup/log10}
## @end defmethod
## Author: Oliver Heimlich
## Keywords: interval
## Created: 2014-10-04
function result = log (x)
if (nargin ~= 1)
print_usage ();
return
endif
x = intersect (x, infsup (0, inf));
## log is monotonically increasing from (0, -inf) to (inf, inf)
l = mpfr_function_d ('log', -inf, x.inf); # this works for empty intervals
u = mpfr_function_d ('log', +inf, x.sup); # ... this does not
l (x.sup == 0) = inf;
u (isempty (x) | x.sup == 0) = -inf;
result = infsup (l, u);
endfunction
%!test "from the documentation string";
%! assert (log (infsup (2)) == "[0x1.62E42FEFA39EFp-1, 0x1.62E42FEFA39Fp-1]");
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