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# blk_lex

## (Toolbox/blk_lex.m in BrainStorm 2.0 (Alpha))

### Function Synopsis

    B = blk_lex(A,n);

### Help Text

    BLK_LEX - Lexicographically order the submatrices in A
     function B = blk_lex(A,n);
     Form B from the first n columns of A.  Concatenate below B the next n
      columns of A.  Repeat for all submatrices of size n.
     Effectively a block form of A(:), such that A(:) == blk_lex(A,1);
     If A is m x b*n, where b is the number of submatrices,
      then B =blk_lex(A,n) is m*b x n.
     The reverse operation is A = blk_lex(B',m)';

     See also BLK_RESHAPE, BLK_TRANS

### Cross-Reference Information

This function is called by

    os_meg                             C:\BrainStorm_2001\Toolbox\os_meg.m

### Listing of function C:\BrainStorm_2001\Toolbox\blk_lex.m

    function B = blk_lex(A,n);
    %BLK_LEX - Lexicographically order the submatrices in A
    % function B = blk_lex(A,n);
    % Form B from the first n columns of A.  Concatenate below B the next n
    %  columns of A.  Repeat for all submatrices of size n.
    % Effectively a block form of A(:), such that A(:) == blk_lex(A,1);
    % If A is m x b*n, where b is the number of submatrices,
    %  then B =blk_lex(A,n) is m*b x n.
    % The reverse operation is A = blk_lex(B',m)';
    %
    % See also BLK_RESHAPE, BLK_TRANS

    %<autobegin> ---------------------- 14-Jun-2004 17:09:49 -----------------------
    % --------- Automatically Generated Comments Block Using AUTO_COMMENTS ---------
    %
    % CATEGORY: Utility - Numeric
    %
    % At Check-in: $Author: Mosher $  $Revision: 16 $  $Date: 6/14/04 3:37p $
    %
    % This software is part of BrainStorm Toolbox Version 2.0 (Alpha) 14-Jun-2004
    %
    % Principal Investigators and Developers:
    % ** Richard M. Leahy, PhD, Signal & Image Processing Institute,
    %    University of Southern California, Los Angeles, CA
    % ** John C. Mosher, PhD, Biophysics Group,
    %    Los Alamos National Laboratory, Los Alamos, NM
    % ** Sylvain Baillet, PhD, Cognitive Neuroscience & Brain Imaging Laboratory,
    %    CNRS, Hopital de la Salpetriere, Paris, France
    %
    % See BrainStorm website at http://neuroimage.usc.edu for further information.
    %
    % Copyright (c) 2004 BrainStorm by the University of Southern California
    % This software distributed  under the terms of the GNU General Public License
    % as published by the Free Software Foundation. Further details on the GPL
    % license can be found at http://www.gnu.org/copyleft/gpl.html .
    %
    % FOR RESEARCH PURPOSES ONLY. THE SOFTWARE IS PROVIDED "AS IS," AND THE
    % UNIVERSITY OF SOUTHERN CALIFORNIA AND ITS COLLABORATORS DO NOT MAKE ANY
    % WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO WARRANTIES OF
    % MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, NOR DO THEY ASSUME ANY
    % LIABILITY OR RESPONSIBILITY FOR THE USE OF THIS SOFTWARE.
    %<autoend> ------------------------ 14-Jun-2004 17:09:49 -----------------------

    % ----------------------------- Script History ---------------------------------
    % Author: John C. Mosher, Ph.D.
    % September 6, 1995 author
    % JCM 19-May-2004  Comments cleaning
    % ----------------------------- Script History ---------------------------------

    nA = size(A,2);            % how many columns in A
    if(rem(nA,n)),
      error('Matrix does not have an integral number of submatrices.')
    end

    ndx = [1:nA]';             % indexing each column
    blocks = nA/n;            % how many submatrices
    % Form such that the ith row corresponds to the set of ith columns in each
    %  submatrix.
    ndx = reshape(ndx,n,blocks);
    % transpose and lexicographically order.
    ndx = ndx';
    ndx = ndx(:)';
    % The ith set of blocks columns corresponds to the ith column of each block
    B = A(:,ndx);
    % now reshape for final result
    B = reshape(B,size(A,1)*blocks,n);

    return

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