function [sys, x0] = animcp1(t, x, u, flag, action)
%ANIMCP1 Animation of CP (cart & pole) system with changing pole length.
%   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; which adds difficulty to the control task.
%
%   If the target position is chosen as mouse-driven, you can click your
%   mouse inside the green triangle to move it to another position.
%   Also clicking "Show Trails" lets you have an idea of how the pole 
%   length changes.
%
%   Animation S-function: animcp1.m
%   SIMULINK file: slcp1.m

%   Roger Jang, 10-28-94
%   Copyright 1994-2004 The MathWorks, Inc.
%   $Revision: 1.16.2.3 $  $Date: 2004/04/10 23:15:13 $

%   User data convention:
%   userdata = get(AnimCpFigH, 'userdata');
%   userdata(1, :) --> handles for standard SL gui control 
%   userdata(2, :) --> handles for additional gui control 
%   userdata(3, :) --> handles for animation objects

global AnimCpFigH AnimCpFigTitle AnimCpAxisH

if ~isempty(flag) & flag == 2,
    if any(get(0, 'children') == AnimCpFigH),
    if strcmp(get(AnimCpFigH, 'Name'), AnimCpFigTitle),
    theta = u(1); pos = u(2); curr_force = u(3); curr_ref = u(4);
    tmp = get(AnimCpFigH, 'userdata');
    objectH = tmp(3, :);

    % During simulation disenable the Target Position pop-up menu
    kids = get(AnimCpFigH,'Children');
    PopUpMenuHndl = findobj(kids,'Tag','SourceSelect');
    set(PopUpMenuHndl,'enable','off');

    % ====== update cart
    cartH = objectH(1);
    cart = get(cartH, 'userdata');
    new_cart = cart + pos; 
    set(cartH, 'xdata', real(new_cart), 'ydata', imag(new_cart));
    % ====== update pole
    %pole_length = u(5);
    %pole_radius = 0.02;
    %pole = pole_radius*[-1 1 1 -1 -1] + ...
    %   j*(pole_length/2*[-1 -1 1 1 -1]+pole_length/2);
    pole = 0.02*[-1 1 1 -1 -1] + j*(u(5)/2*[-1 -1 1 1 -1]+u(5)/2);
    poleH = objectH(2);
    new_pole = pole*exp(-j*theta) + pos;
    set(poleH, 'xdata', real(new_pole), 'ydata', imag(new_pole));
    % ====== update force arrow
    cart_length = abs(real(cart(1)))*2;
    cart_height = abs(imag(cart(1)));
    forceH = objectH(3);
    force = get(forceH, 'userdata');
    new_force = curr_force/4*force + pos - j*cart_height/2 ...
        - sign(curr_force)*cart_length/2;
    set(forceH, 'xdata', real(new_force), 'ydata', imag(new_force));
    % ====== update reference triangle if not dragging
    refH = objectH(4);
    ref = get(refH, 'userdata');
    new_ref = ref + curr_ref;
    set(refH, 'xdata', real(new_ref), 'ydata', imag(new_ref));
    % ====== update time 
    tmp = get(AnimCpFigH, 'userdata');
    timeH = tmp(1, 6);
    set(timeH, 'String', ['Time: ', sprintf('%.2f', t)]);
    end
    end
    % ====== return nothing
    sys = [];
    x0=[];
    drawnow;    % for invoking with rk45()
elseif ~isempty(flag) & flag == 9,   % When simulation stops ...
    % ====== change labels of standard UI controls
    if any(get(0, 'children') == AnimCpFigH),
    if strcmp(get(AnimCpFigH, 'Name'), AnimCpFigTitle),
    tmp = get(AnimCpFigH, 'userdata');
    set(tmp(1, 1), 'visible', 'on');    % start
    set(tmp(1, 2:5), 'visible', 'off');

    % At end of simulation re-enable the Target Position pop-up menu
    kids = get(AnimCpFigH,'Children');
    PopUpMenuHndl = findobj(kids,'Tag','SourceSelect');
    set(PopUpMenuHndl,'enable','on'); 

    end
    end
elseif ~isempty(flag) & flag == 0,
    % ====== find animation block & figure
    [winName] = bdroot(gcs);
    AnimCpFigTitle = [winName, ': Cart & Pole Animation'];
    [flag, AnimCpFigH] = figflag(AnimCpFigTitle);
    % ====== % No figure, initialize everything
    if ~flag,
        ui_row_n = 2;   % No. of UI rows
        % ###### default UI settings for SIMUINK ######
        AnimCpFigH = figure( ...
            'Name', AnimCpFigTitle, ...
            'NumberTitle', 'off',...
            'DockControls','off');
        figPos = get(AnimCpFigH, 'position');
        % ====== proportion of UI frame and axes
        ui_area = 0.2;
        axis_area = 1-ui_area;
        % ====== animation area 
        axisPos = [0 figPos(4)*ui_area figPos(3) figPos(4)*axis_area];
        % weird thing: if you don't use normalized unit for
        % axes, patch for ground doesn't appear
        axisPos = axisPos./[figPos(3) figPos(4) figPos(3) figPos(4)];
        AnimCpAxisH = ...
            axes('unit', 'normal', 'pos', axisPos, 'visible', 'off');
        % ====== background frame
        coverPos = [0 0 figPos(3) figPos(4)*ui_area];
        [frameH, framePos] = uiarray(coverPos, 1, 1, 0);
        % ====== rows for UI controls
        spacing = 5;
        [H, Pos] = uiarray(framePos, ui_row_n, 1, spacing);
        % ====== split lower-most rows into 2 uneven regions
        delete(H(2));
        [tmpH, tmpPos] = uiarray(Pos(2,:), 1, 6, 0, spacing);
        % lower left frame
        delete(tmpH(2:4));
        lPos = tmpPos(1, :);
        lPos(3) = 4*lPos(3)+3*spacing;
        set(tmpH(1), 'pos', lPos);
        % lower right frame
        delete(tmpH(6));
        rPos = tmpPos(5, :);
        rPos(3) = 2*rPos(3)+spacing;
        set(tmpH(5), 'pos', rPos);
        % ====== lower-right UI's (same for all SL animation)
        cb1 = [mfilename '([], [], [], [], ''info'')'];
        cb2 = [mfilename '([], [], [], [], ''close'')'];
        [lrH, lrPos] = uiarray(rPos, 1, 2, spacing, spacing, ...
            str2mat('push', 'push'), ...
            str2mat(cb1, cb2), ...
            str2mat('Help', 'Close'));
        infoH = lrH(1);
        closeH = lrH(2);
        % ====== lower-left UI's (same for all SL animation)
        cb1 = '';
        cb2 = [mfilename '([], [], [], [], ''start_sl'')'];
        cb3 = '';
        cb4 = '';
        [llH, llPos] = uiarray(lPos, 1, 4, spacing, spacing, ...
            str2mat('text', 'push', 'text', 'text'), ...
            str2mat(cb1, cb2, cb3, cb4), ...
            str2mat('t = 0', 'Start Simulation ...','',''));
        timeH = llH(1);
        % ====== extend the width of start button
        delete(llH(3:4));
        startH = llH(2);
        startPos = llPos(2,:);
        startPos(3) = 3*startPos(3)+2*spacing;
        set(startH, 'pos', startPos);
        % ====== create stop and pause (under start)
        cb1 = [mfilename '([], [], [], [], ''stop_sl'')'];
        cb2 = [mfilename '([], [], [], [], ''pause_sl'')'];
        cb3 = '';
        [h, pos] = uiarray(startPos, 1, 3, 0,spacing,'push', ...
            str2mat(cb1, cb2, cb3), ...
            str2mat('Stop', 'Pause ...', ''));
        set(h, 'visible', 'off');
        stopH = h(1); pauseH = h(2);
        % ====== extend the width of pause button
        delete(h(3));
        pausePos = pos(2, :);
        pausePos(3) = 2*pausePos(3)+spacing;
        set(pauseH, 'pos', pausePos);
        % ===== create continue and step (under pause)
        cb1 = [mfilename '([], [], [], [], ''continue_sl'')'];
        cb2 = [mfilename '([], [], [], [], ''step_sl'')'];
        [h, pos] = uiarray(pausePos, 1, 2, 0, spacing, ...
            'push', ...
            str2mat(cb1, cb2), ...
            str2mat('Continue', 'Step'));
        set(h, 'visible', 'off');
        contH = h(1); stepH = h(2);
        %===== put UI handles into current figure's user data 
        tmp = [startH stopH pauseH contH stepH timeH -1 -1 -1 -1];
        set(AnimCpFigH, 'userdata', tmp);

        % ###### additional UI settings ######
        % ====== The upper UI controls (Specific to each animation)
        cb1 = [mfilename '([], [], [], [], ''show_trail'')'];
        cb2 = [mfilename '([], [], [], [], ''clear_trail'')'];
        cb3 = '';
        cb4 = [mfilename '([], [], [], [], ''target_pos'')'];

        string1 = 'Show Trails';
        string2 = 'Clear Trails';
        string3 = 'Target Position:';
        string4 = 'Sinusoid Wave|Square Wave|Saw Wave|Mouse-Driven';

        [upH, upPos] = uiarray(Pos(1,:), 1, 4, spacing, 2*spacing, ...
            str2mat('check', 'push', 'text', 'popup'), ...
            str2mat(cb1, cb2, cb3, cb4), ...
            str2mat(string1, string2, string3, string4));
        set(upH(3), 'HorizontalAlignment', 'right');
        signalH = upH(4);
        % Set the Tag of the pop-up menu so it can be found and disenabled during simulation
        set(signalH,'Tag','SourceSelect');
        dispmodeH = upH(1);
        % The value of signalH should match that of SL block
        [winName] = bdroot(gcs);
        signal_block = [winName, '/Target Position'];
        signal_value = get_param(signal_block, 'WaveForm');
        if strcmp(signal_value, 'sine'),
            set(signalH, 'value', 1);
        elseif strcmp(signal_value, 'square'),