Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / general-1.3.1 / safeprod.m

diff --git a/octave_packages/general-1.3.1/safeprod.m b/octave_packages/general-1.3.1/safeprod.m
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+## Copyright (C) 2008 VZLU Prague, a.s., Czech Republic
+##
+## 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} {@var{p} =} safeprod (@var{x}, @var{dim})
+## @deftypefnx{Function File} {[@var{p}, @var{e}] =} safeprod (@var{x}, @var{dim})
+## This function forms product(s) of elements of the array @var{x} along the dimension 
+## specified by @var{dim}, analogically to @code{prod}, but avoids overflows and underflows 
+## if possible. If called with 2 output arguments, @var{p} and @var{e} are computed 
+## so that the product is @code{@var{p} * 2^@var{e}}.
+## @seealso{prod,log2}
+## @end deftypefn
+
+## Author: Jaroslav Hajek <highegg@gmail.com>
+
+function [p, e] = safeprod (x, dim)
+  if (nargin < 1 || nargin > 2)
+    print_usage ();
+  endif
+
+  if (nargin < 2)
+    if (rows(x) == 1)
+      dim = 2;
+    else
+      dim = 1;
+    endif
+  endif
+
+  % try the normal algorithm first
+  if (nargout < 2) 
+    p = prod (x, dim);
+  else
+    p = 0;
+  endif
+
+  % 0, Inf and NaN are possibly problematic results. If detected, use the safe
+  % formula.
+
+  flag = (p == 0 | ! isfinite (p));
+
+  if (any (flag(:)))
+    [f, e] = log2 (x);
+    p = prod (f, dim);
+    e = sum (e, dim);
+    if (nargout < 2)
+      p = p .* 2.^e;
+    endif
+  endif
+
+endfunction