% STK_SAMPLING_HALTON_RR2 generates points from the Halton/RR2 sequence
%
% CALL: X = stk_sampling_halton_rr2 (N, D)
%
%    computes the first N terms of the D-dimensional RR2-scrambled Halton
%    sequence.
%
% REFERENCE
%
%    Ladislav Kocis and William J. Whiten, "Computational investigations of low
%    discrepancy sequences", ACM Transactions on Mathematical Software,
%    23(2):266-294, 1997.  http://dx.doi.org/10.1145/264029.264064
%
% SEE ALSO: __stk_sampling_vdc_rr2__

% Copyright Notice
%
%    Copyright  (C) 2017, 2018 CentraleSupelec
%    Copyright  (C) 2014 SUPELEC
%    Copyright  (C) 2013 Alexandra Krauth, Elham Rahali & SUPELEC
%
%    Authors:  Julien Bect       <julien.bect@centralesupelec.fr>
%              Alexandra Krauth  <alexandrakrauth@gmail.com>
%              Elham Rahali      <elham.rahali@gmail.com>

% Copying Permission Statement
%
%    This file is part of
%
%            STK: a Small (Matlab/Octave) Toolbox for Kriging
%               (http://sourceforge.net/projects/kriging)
%
%    STK 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.
%
%    STK 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 STK.  If not, see <http://www.gnu.org/licenses/>.

function x = stk_sampling_halton_rr2 (n, d, box)

% Read argument dim
if (nargin < 2) || ((nargin < 3) && (isempty (d)))
    d = 1;  % Default dimension
elseif (nargin > 2) && (~ isempty (box))
    d = size (box, 2);
end

% Read argument 'box'
if (nargin < 3) || isempty (box)
    colnames = {};
else
    box = stk_hrect (box);  % convert input argument to a proper box
    colnames = box.colnames;
end

xdata = zeros (n, d);
for j = 1:d,
    xdata(:, j) = double (__stk_sampling_vdc_rr2__ (n, j));
end

x = stk_dataframe (xdata, colnames);

if nargin > 2,
    x = stk_rescale (x, [], box);
end

end % function


%!error stk_sampling_halton_rr2 ()               % nargin < 1

%!test
%! n = 300; d = 25;
%! x = stk_sampling_halton_rr2 (n, d);
%! assert (isequal (size (x), [n d]))

%!test
%! x = stk_sampling_halton_rr2 (1000, 3);
%! y = double (x(end, :));
%! yref = [0.9052734375 0.028349336991312 0.74848];
%! assert (stk_isequal_tolrel (y, yref, 1e-13));

%%
% Check that column names are properly set, if available in box

%!test
%! dim = 2;  box = stk_hrect (dim);
%! x = stk_sampling_halton_rr2 (5, dim, box);
%! assert (isequal (x.colnames, {}));

%!test
%! dim = 2;  cn = {'W', 'H'};  box = stk_hrect (dim, cn);
%! x = stk_sampling_halton_rr2 (5, dim, box);
%! assert (isequal (x.colnames, cn));

%%
% Comparison with Scilab+lowdisc

% % Matlab/Octave STK test script
%
% NREP = 10;
% M = 1e5;
% DIM = 20;
%
% tic;
% for i = 1:NREP
%     x = stk_sampling_halton_rr2(M, DIM);
% end;
% t1 = toc/NREP;
% fprintf('time elapsed: %.2e seconds\n', t1);
%
% fprintf('%.15f\n', x(1:5, 2))

% // Scilab lowdisc test script
%
% NREP = 10;
% M = 1e5;
% DIM = 20;
%
% tic();
% for i = 1:NREP,
%     rng = lowdisc_new("halton");
%     rng = lowdisc_configure(rng, "-dimension", DIM);
%     rng = lowdisc_configure(rng, "-scrambling", "RR2");
%     rng = lowdisc_startup(rng);
%     [rng, x] = lowdisc_next(rng, M);
%     rng = lowdisc_destroy(rng);
% end
% t = toc() / NREP
%
% mprintf('%.15f\n', x(1:9, 2))
