--- /dev/null
+function FLAG = flag_accuracy_level(i)
+% FLAG_ACCURACY_LEVEL sets and gets accuracy level
+% used in SUMSKIPNAN_MEX and COVM_MEX
+% The error margin of the naive summation is N*eps (N is the number of samples),
+% the error margin is only 2*eps if Kahan's summation is used [1].
+%
+% 0: maximum speed [default]
+% accuracy of double (64bit) with naive summation (error = N*2^-52)
+% 1: accuracy of extended (80bit) with naive summation (error = N*2^-64)
+% 2: accuracy of double (64bit) with Kahan summation (error = 2^-52)
+% 3: accuracy of extended (80bit) with Kahan summation (error = 2^-64)
+%
+% Please note, level 3 might be equally accurate but slower than 1 or 2 on
+% some platforms. In order to determine what is good for you, you might want
+% to run ACCTEST.
+%
+% FLAG = flag_accuracy_level()
+% gets current level
+% flag_accuracy_level(FLAG)
+% sets accuracy level
+%
+% see also: ACCTEST
+%
+% Reference:
+% [1] David Goldberg,
+% What Every Computer Scientist Should Know About Floating-Point Arithmetic
+% ACM Computing Surveys, Vol 23, No 1, March 1991.
+
+
+% 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, write to the Free Software
+% Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+% $Id$
+% Copyright (C) 2009 by Alois Schloegl <alois.schloegl@gmail.com>
+% This function is part of the NaN-toolbox
+% http://pub.ist.ac.at/~schloegl/matlab/NaN/
+
+
+persistent FLAG_ACCURACY_LEVEL;
+
+%% if strcmp(version,'3.6'), FLAG_ACCURACY_LEVEL=1; end; %% hack for the use with Freemat3.6
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% set the default accuracy level for your platform, ACCTEST might help to determine the optimum for your platform.
+%% If you use Matlab, use level 0 or 2; 1 and 3 are much slower but do not show a better accuracy
+%% Octave seems to be able to use all 4 levels, were the differences of accuracy between succeeding levels become smaller
+DEFAULT_ACCURACY_LEVEL = 0; %% maximum speed, accuracy sufficient for most needs.
+%% DEFAULT_ACCURACY_LEVEL = 2; %% slower, but better accuracy for: AMDx64 Opteron, Phenom, Intel Pentium
+%% DEFAULT_ACCURACY_LEVEL = 1; %% slower, but better accuracy for: Octave on Intel Atom (no improvement with Matlab, just slower)
+%% DEFAULT_ACCURACY_LEVEL = 3; %% similar accuracy than 1 or 2 (depending on platform) but even slower.
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+
+%%% set DEFAULT value of FLAG
+if isempty(FLAG_ACCURACY_LEVEL),
+ FLAG_ACCURACY_LEVEL = DEFAULT_ACCURACY_LEVEL;
+end;
+
+if nargin>0,
+ if (i>3), i=3; end;
+ if (i<0), i=0; end;
+ FLAG_ACCURACY_LEVEL = double(i);
+end;
+FLAG = FLAG_ACCURACY_LEVEL;
+