Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / nan-2.5.5 / flag_accuracy_level.m

diff --git a/octave_packages/nan-2.5.5/flag_accuracy_level.m b/octave_packages/nan-2.5.5/flag_accuracy_level.m
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+++ b/octave_packages/nan-2.5.5/flag_accuracy_level.m
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+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;
+