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# get_gain

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

### Function Synopsis

    A = get_gain(fid,ndx);

### Help Text

    GET_GAIN - Get a set of source foward fields from a .bin gain matrix file
     function A = get_gain(fid,ndx);
     Get a set of source foward fields A from a .bin gain matrix file
     INPUTS
           fid : a file identifier following a fopen call on a valid binary gain matrix file
           ndx : vector array of source indices for which the forward fields are requested
     OUTPUTS
           A   : array of requested forward fields

     The user is responsible for opening the file in the proper machine format.

     For head model matrices, this routine should only be accessed from read_gain,
     so that a consistent machine format is used to read the file.

     See also READ_GAIN, LOAD_RAW, SAVE_RAW

### Cross-Reference Information

This function calls

    offset                             C:\BrainStorm_2001\Toolbox\offset.m

This function is called by

    mritool_cb                         C:\BrainStorm_2001\Toolbox\mritool_cb.m
    read_gain                          C:\BrainStorm_2001\Toolbox\read_gain.m

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

    function A = get_gain(fid,ndx);
    %GET_GAIN - Get a set of source foward fields from a .bin gain matrix file
    % function A = get_gain(fid,ndx);
    % Get a set of source foward fields A from a .bin gain matrix file
    % INPUTS
    %       fid : a file identifier following a fopen call on a valid binary gain matrix file
    %       ndx : vector array of source indices for which the forward fields are requested
    % OUTPUTS
    %       A   : array of requested forward fields
    %
    % The user is responsible for opening the file in the proper machine format.
    %
    % For head model matrices, this routine should only be accessed from read_gain,
    % so that a consistent machine format is used to read the file.
    %
    % See also READ_GAIN, LOAD_RAW, SAVE_RAW

    %<autobegin> ---------------------- 08-Jun-2004 15:11:19 -----------------------
    % --------- Automatically Generated Comments Block Using AUTO_COMMENTS ---------
    %
    % CATEGORY: Forward Modeling
    %
    % At Check-in: $Author: Mosher $  $Revision: 17 $  $Date: 6/08/04 1:38p $
    %
    % This software is part of BrainStorm Toolbox Version 2.0 (Alpha) 28-May-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> ------------------------ 08-Jun-2004 15:11:19 -----------------------

    % \------------------------------------------------------/
    % | *** Sylvain Baillet, Ph.D.                           |
    % | Cognitive Neuroscience & Brain Imaging Laboratory    |
    % | CNRS UPR640 - LENA                                   |
    % | Hopital de la Salpetriere, Paris, France             |
    % | sylvain.baillet@chups.jussieu.fr                     |
    % \------------------------------------------------------/
    %
    % Date of creation: October 2002
    % Script History -----------------------------------------------------------------------------------
    %---------------------------------------------------------------------------------------------------

    frewind(fid);

    rows = fread(fid,1,'uint32');

    if nargin == 2
       cols = length(ndx);

       A = zeros(rows,cols);

       for i = 1:cols,
          % 4 bytes per element, find starting point
          offset = 4 + (ndx(i)-1)*rows*4;
          status = fseek(fid,offset,'bof');
          if(status == -1),
             error(sprintf('Error reading file at column %.0f',i));
          end

          A(:,i) = fread(fid,[rows,1],'float32');

       end

       return

    else % ndx is not specified: read the whole matrix

       offset = 4;
       status = fseek(fid,offset,'bof');
       fbegin = ftell(fid);
       status = fseek(fid,0,'eof');
       fend = ftell(fid);

       frewind(fid);
       offset = 4;
       status = fseek(fid,offset,'bof');

       cols = (fend - fbegin + 1) / (4* rows); % Number of sources / columns

       A = fread(fid,[rows, cols],'float32');

    end

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