/usr/share/octave/packages/interval-2.1.0/@infsup/log1p.m is in octave-interval 2.1.0-2.
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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
## @defmethod {@@infsup} log1p (@var{X})
##
## Compute @code{log (1 + @var{X})} accurately in the neighborhood of zero.
##
## The function is only defined where @var{X} is greater than -1.
##
## Accuracy: The result is a tight enclosure.
##
## @example
## @group
## log1p (infsup (eps))
## @result{} ans ⊂ [2.2204e-16, 2.2205e-16]
## @end group
## @end example
## @seealso{@@infsup/exp, @@infsup/log}
## @end defmethod
## Author: Oliver Heimlich
## Keywords: interval
## Created: 2015-02-20
function x = log1p (x)
if (nargin ~= 1)
print_usage ();
return
endif
x = intersect (x, infsup (-1, inf));
## log is monotonically increasing from (-1, -inf) to (inf, inf)
if (__check_crlibm__ ())
l = crlibm_function ('log1p', -inf, x.inf); # this works for empty intervals
u = crlibm_function ('log1p', +inf, x.sup); # ... this does not
else
l = mpfr_function_d ('log1p', -inf, x.inf); # this works for empty intervals
u = mpfr_function_d ('log1p', +inf, x.sup); # ... this does not
endif
l(x.sup == -1) = inf;
l(l == 0) = -0;
u(isempty (x) | x.sup == -1) = -inf;
x.inf = l;
x.sup = u;
endfunction
%!# from the documentation string
%!assert (log1p (infsup (eps)) == "[0x1.FFFFFFFFFFFFFp-53, 0x1p-52]");
%!# correct use of signed zeros
%!test
%! x = log1p (infsup (0));
%! assert (signbit (inf (x)));
%! assert (not (signbit (sup (x))));
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