set(signalH, 'value', 2);
        elseif strcmp(signal_value, 'sawtooth'),
            set(signalH, 'value', 3);
        else
            error('Unknown signal generator!');
        end
        constant_block = [winName, '/Constant'];
        if str2double(get_param(constant_block, 'value')) < 0,
            set(signalH, 'value', 4);
        end
        % ====== Appending handles as the second row of userdata
        tmp = [signalH dispmodeH -1 -1 -1 -1 -1 -1 -1 -1];
        set(AnimCpFigH, 'userdata', [get(AnimCpFigH, 'userdata'); tmp]);

        % ###### animation objects ######
        % ====== cart
        cart_height = 0.2;
        cart_length = 0.4;
        cart = cart_length/2*[-1 1 1 -1 -1] + ...
            j*(cart_height/2*[-1 -1 1 1 -1]-cart_height/2+.005);
        cartH = patch(real(cart), imag(cart), 'm');
        set(cartH, 'erase', 'xor');
        set(cartH, 'userdata', cart);
        % ====== pole
        pole_length = 1; % this must be the same as plant block
        pole_radius = 0.02;
        pole = pole_radius*[-1 1 1 -1 -1] + ...
            j*(pole_length/2*[-1 -1 1 1 -1]+pole_length/2 + .003);
        poleH = patch(real(pole), imag(pole), 'y');
        set(poleH, 'erase', 'xor', 'clipping', 'off');
        set(poleH, 'userdata', pole);
        % ====== force arrow
        force_x = [-1 0 nan -0.1 0 -0.1];
        force_y = [0 0 nan 0.1 0 -0.1];
        force = force_x + j*force_y;
        forceH = line(real(force), imag(force), ...
            'erase', 'xor', 'color', 'c', 'clip', 'off');
        set(forceH, 'userdata', force, ...
            'xdata', [0], 'ydata', [0]);
        % ====== reference triangle
        ref = cart_length/2*[-1 1 0 -1] + ...
            j*cart_height*([0 0 1 0] - 1.1);
        ref = ref - 2*j*cart_height;
        refH = line(real(ref), imag(ref));
        set(refH, 'color', 'g', 'linewidth', 2);
    %   refH = patch(real(ref), imag(ref), 'g');
        set(refH, 'erase', 'background');
        set(refH, 'userdata', ref);
        % ====== axis settings
        pos_range = [-2 2];
        set(AnimCpAxisH, 'clim', [1 64], ...
            'xlim', pos_range, ...
            'ylim', [-cart_height 1*1.2], ...
            'box', 'on');
        axis equal;
        set(AnimCpAxisH, 'visible', 'off');
        % ====== colormap settings for floor
        colormap(gray); %  To assign correct patch color
        patch([pos_range -pos_range], ...
            cart_height*[-2 -2 -1 -1], [10 10 55 55]);
        % ====== append the handles as third row of userdata
        tmp = [cartH poleH forceH refH -1 -1 -1 -1 -1 -1];
        set(AnimCpFigH, 'userdata', [get(AnimCpFigH, 'userdata'); tmp]);
        % ====== change to normalized units
        set(findobj(AnimCpFigH,'Units','pixels'), 'Units','normalized');
        % ====== move the reference triangle by mouse
        % action when button is first pushed down
        action1 = [mfilename '([], [], [], [], ''mouse_action'')'];
        action2 = action1;
        % actions after the mouse is pushed down  
        % action when button is released
        action3 = action1;

        % temporary storage for the recall in the down_action
        set(AnimCpAxisH,'UserData',action2);

        % set action when the mouse is pushed down
        down_action=[ ...
            'set(AnimCpFigH,''WindowButtonMotionFcn'',get(AnimCpAxisH,''UserData''));' ...
            action1];
        set(AnimCpFigH,'WindowButtonDownFcn',down_action);

        % set action when the mouse is released
        up_action=[ ...
            'set(AnimCpFigH,''WindowButtonMotionFcn'','' '');', action3];
        set(AnimCpFigH,'WindowButtonUpFcn',up_action);


    end
    % ====== change labels of standard UI controls
    tmp = get(AnimCpFigH, 'userdata');
    set(tmp(3, 1:4), 'erasemode', 'xor');
    set(tmp(1, 1), 'visible', 'off');
    set(tmp(1, 2:3), 'visible', 'on');
    sys = [0 0 0 5 0 0];
    x0=[];
    set(AnimCpFigH, 'HandleVisibility', 'on');
elseif nargin == 5, % for callbacks of GUI
    % ###### standard UI controls
    if strcmp(action, 'start_sl'),
        tmp = get(AnimCpFigH, 'userdata');
        set(tmp(1, 1), 'visible', 'off');
        set(tmp(1, 2:3), 'visible', 'on');
        [winName] = bdroot(gcs);
        set(tmp(3, 1:4), 'erasemode', 'xor');
        refresh(AnimCpFigH);
        set_param(winName, 'SimulationCommand', 'start');
    elseif strcmp(action, 'stop_sl'),
        tmp = get(AnimCpFigH, 'userdata');
        set(tmp(1, 1), 'visible', 'on');
        set(tmp(1, 2:5), 'visible', 'off');
        [winName] = bdroot(gcs);
        set_param(winName, 'SimulationCommand', 'stop');
    elseif strcmp(action, 'pause_sl'),
        tmp = get(AnimCpFigH, 'userdata');
        set(tmp(1, 3), 'visible', 'off');
        set(tmp(1, 4:5), 'visible', 'on');
        [winName] = bdroot(gcs);
        set_param(winName, 'SimulationCommand', 'pause');
    elseif strcmp(action, 'step_sl'),
        [winName] = bdroot(gcs);
        set_param(winName, 'SimulationCommand', 'step');
    elseif strcmp(action, 'continue_sl'),
        tmp = get(AnimCpFigH, 'userdata');
        set(tmp(1, 3), 'visible', 'on');
        set(tmp(1, 4:5), 'visible', 'off');
        [winName] = bdroot(gcs);
        set_param(winName, 'SimulationCommand', 'continue');
    elseif strcmp(action, 'info'),
        helpwin(mfilename);
    %   title = get(AnimCpFigH, 'Name');
    %   content = ...
    %   ['                                                    '
    %    ' Animation of the cart & pole (CP) system, where a  '
    %    ' Sugeno-type fuzzy controller is used to balance the'
    %    ' pole as well as move the cart to a target position '
    %    ' indicated by the green triangle. This system is    '
    %    ' different from the ordinary CP system in that the  '
    %    ' pole length is time varying; this adds difficulty  '
    %    ' to the control task.                               '
    %    '                                                    '
    %    ' Animation S-function: animcp1.m                    '
    %    ' SIMULINK file: slcp1.m                             '];
    %   fhelpfun(title, content);        
    elseif strcmp(action, 'close'),
%       [winName, sysName] = bdroot(gcs);
%       set_param(winName, 'Simulation running', 'stop');
        delete(AnimCpFigH);

    % ###### additional UI controls
    elseif strcmp(action, 'target_pos'),
        [winName] = bdroot(gcs);
        if strcmp(get_param(winName,'SimulationStatus'),'running')
            error('Cannot change target position when simulation is running')
        end
        signal_block = [winName, '/Target Position'];
        constant_block = [winName, '/Constant'];
        tmp = get(AnimCpFigH, 'userdata');
        signalH = tmp(2, 1);
        signal = get(signalH, 'value');
        if signal == 1, % sinusoid wave
            set_param(signal_block, 'wave', 'sine');
            set_param(constant_block, 'value', '1');
        elseif signal == 2, % square wave
            set_param(signal_block, 'wave', 'square');
            set_param(constant_block, 'value', '1');
        elseif signal == 3, % saw wave
            set_param(signal_block, 'wave', 'sawtooth');
            set_param(constant_block, 'value', '1');
        elseif signal == 4, % mouse-driven
            set_param(constant_block, 'value', '-1');
        else
            error('Unknown wave option!');
        end
    elseif strcmp(action, 'show_trail'),
        tmp = get(AnimCpFigH, 'userdata');
        dispmodeH = tmp(2, 2);
        objectH = tmp(3, 1:4);
        dispmode = get(dispmodeH, 'value');
        if dispmode == 0,   % xor
            set(objectH, 'erasemode', 'xor');
            refresh(AnimCpFigH);
           % set(AnimCpFigH, 'color', get(AnimCpFigH, 'color'));
        else
            set(objectH, 'erasemode', 'none');
        end
    elseif strcmp(action, 'clear_trail'),
        refresh(AnimCpFigH);
    %    set(AnimCpFigH, 'color', get(AnimCpFigH, 'color'));
    elseif strcmp(action, 'mouse_action')
        [winName] = bdroot(gcs);
        if str2double(get_param([winName, '/Constant'], 'value')) < 0,
            curr_info = get(AnimCpAxisH, 'CurrentPoint');
            tmp = get(AnimCpFigH, 'UserData');
            refH = tmp(3, 4);

            desired_pos = curr_info(1,1);
            desired_pos = min(max(desired_pos, -1.5), 1.5);
            ref = get(refH, 'userdata');
            new_ref = ref + desired_pos;
            set(refH, 'xdata', real(new_ref), 'ydata', imag(new_ref));
            [windowname] = bdroot(gcs);
            set_param([windowname, '/Target Position',13,'(Mouse-Driven)'],...
                'value', num2str(desired_pos));
        end
    else
        fprintf('Unknown action string: %s.\n', action);
    end
end