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: tripleangle.m
    path of file: ./repos/robotics-toolbox-matlab/Apps
    
    the code of the file until where you have to start completion: % TRIPLEANGLE Visualize triple angle rotations
%
% TRIPLEANGLE, by itself, displays a simple GUI with three angle sliders
% and a set of axes showing th
    
function tripleangle_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject    handle to figure
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
% varargin   command line arguments to tripleang (see VARARGIN)

% Choose default command line output for tripleang
handles.output = hObject;

figure(handles.figure1);


% process options
opt.wait = false;
opt.which = {'rpy', 'euler'};

[opt,args] = tb_optparse(opt, varargin);

if length(args) > 0 && ischar(args{1})
    s = args{1};
    try
        set(handles.popupmenu1, 'Value', strfind('xyz', s(1)));
        set(handles.popupmenu2, 'Value', strfind('xyz', s(2)));
        set(handles.popupmenu3, 'Value', strfind('xyz', s(3)));
        if length(args) > 1
            args = args{2:end