You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: osp_onLB.m
    path of file: ./repos/osprey/GUI
    
    the code of the file until where you have to start completion: function osp_onLB( source, ~ ,gui)
%% osp_onLB
%   Callback function on process click on left x voxel direction button.
%
%
%   USAGE:
%       osp_onLeftX( ~, ~ ,gui);
%
%   INPUT:      gui      = gui class containing all handles and the MRSCont 
%
%   OUTPUT:     Changes in gui parameters and MRSCont are written into the
%               gui class
%
%
%   AUTHORS:
%       Dr. Helge Zoellner (Johns Hopkins University, 2020-01-16)
%       hzoelln2@jhmi.edu
%
%   CREDITS:
%       This code is based on numerous functions from the FID-A toolbox by
%       Dr. Jamie Near (McGill University)
%       https://github.com/CIC-methods/FID-A
%       Simpson et al., Magn Reson Med 77:23-33 (2017)
%
%   HISTORY:
%       2021-01-21: First version of the code.
%%% 1. INITIALIZE %%%
    MRSCont = getappdata(gui.figure,'MRSCont');  % Get MRSCont from hidden container in gui class 
    selectedTab = get(gui.layout.tabs, 'Selection');

    % User wants to process the data
%%% 2. UPDATEWINDOW %%%    

    selectedLB = get(source, 'Value');
    MRSCont.opts.cosmetics.LB = selectedLB;

    
function osp_onLB( source, ~ ,gui)
%% osp_onLB
%   Callback function on process click on left x voxel direction button.
%
%
%   USAGE:
%       osp_onLeftX( ~, ~ ,gui);
%
%   INPUT:      gui      = gui class containing all handles and the MRSCont 
%
%   OUTPUT:     Changes in gui parameters and MRSCont are written into the
%               gui class
%
%
%   AUTHORS:
%       Dr. Helge Zoellner (Johns Hopkins University, 2020-01-16)
%       hzoelln2@jhmi.edu
%
%   CREDITS:
%       This code is based on numerous functions from the FID-A toolbox by
%       Dr. Jamie Near (McGill University)
%       https://github.com/CIC-methods/FID-A
%       Simpson et al., Magn Reson Med 77:23-33 (2017)
%
%   HISTORY:
%       2021-01-21: First version of the code.
%%% 1. INITIALIZE %%%
    MRSCont = getappdata(gui.figure,'MRSCont');  % Get MRSCont from hidden container in gui class 
    selectedTab = get(gui.layout.tabs, 'Selection');

    % User wants to process the data
%%% 2. UPDATEWINDOW %%%    

    selectedLB = get(source, 'Value');
    MRSCont.opts.cosmetics.LB = selectedLB;
    set(source, 'Tooltip', ['Exponential Linebroadening (Hz) ' num2str(selectedLB)]);
    setappdata(gui.figure,'MRSCont',MRSCont);   % Write MRSCont into hidden container in gui class 
    osp_updateFitWindow(gui);

end