function output = analyzer(action)
global ocheck eqStrCur eqStrMat indepVar noOfPoints
global newFig noOfPlots curFigure maxPlotNo eqEvalStr
% ANALYZER  equation plotting function.
%   User specifies limits on axes, and inputs the equation.
%
%   Original programmatic layout is adapted from dfield written by John C. Polking, Rice University
%
%   Modified and updated version of written program.
%   Modified and updated by Il-Joong Kil, November 2001
%   Finalised to version 2.0 on 20 Febuary 2002

format long;

if nargin < 1
    action ='initialize';
end

% Initialization sequences
if strcmpi(action,'initialize')
    % Closes all the opened analyzer windows
    figs = get(0,'children');
    for (figno = 1:length(figs))
        nn = get(figs(figno),'name');
        TTT = findstr(nn,'ANALYZER');
        SSS = findstr(nn,'WARNING!!');
        if (~isempty(TTT)|~isempty(SSS)) delete(figs(figno)); end;
    end
    
    % The default differential equation, and Display window.
    Tname    = 't'; equation = 't^2 - 1'; WINvect  = [-5 5 -5 5];
    
    % Main window properties
    dfset = figure('pos',[30 70 470 320],'color',[0.95 0.85 0.75],'CloseRequestFcn','analyzer(''quit'')',...
        'resize','off','name','ANALYZER PLOT DETAILS','numb','off','visible','off','menu','none');
    figure(dfset)

    % Equation field
    frame(1) = uicontrol('style','frame','backgroundcolor',[0.8 0.8 0.9],...
        'pos',[25,205,420,90],'visible','off');
    % Call sequence for the independent variable text field
    tname = [
        'sh = get(gcf,''user'');','sm = get(sh(1),''user'');'...
            'eq = sh(3:7);','wind =sh(8:16);'...
            'Tname=deblank2(get(eq(5),''string''));'...
            'set(eq(5),''string'',Tname);'...
            'set(eq(2),''string'',[''x('', Tname, '') = '']);'...
            'set(wind(2),''string'',[''lower '',Tname,'' = '']);'...
            'set(wind(6),''string'',[''upper '',Tname,'' = '']);'...
            'sm = str2mat(Tname,sm(2,:));','set(sh(1),''user'',sm);'];
    % Call sequence for the equation text field
    xeqn =[
        'sh = get(gcf,''user'');','sm = get(sh(1),''user'');'...
            'eq=sh(3:7);','equation = deblank2(get(eq(3),''string''));'...
            'set(eq(3),''string'',equation);'...
            'sm = str2mat(sm(1,:),equation);','set(sh(1),''user'',sm);'];
    % Label "Enter the equation:"
    eq(1)=uicontrol('style','text','pos',[30 268 410 20],'backgroundcolor',[0.8 0.8 0.9],...
        'horizon','center','string','Enter the equation:','visible','off','fontweight','bold');
    % Label "x(tname) = "
    eq(2) = uicontrol('style','text','pos',[30 245 100 20],'backgroundcolor',[0.8 0.8 0.9],...
        'horizon','right','string',['x(', Tname, ') = '],'visible','off');
    % Text field for eq(2)
    eq(3)=uicontrol('pos',[140 245 270 20],'backgroundcolor','w',...
        'string',equation,'horizon','left','style','edit','call',xeqn,'visible','off');
    % Label "The independent variable is "
    eq(4)=uicontrol('pos',[30 210 200 20],'style','text','backgroundcolor',[0.8 0.8 0.9],...
        'horizon','right','string','The independent variable is ','visible','off');
    % Text field for eq(4)
    eq(5)=uicontrol('pos',[230 210 80 20],'string',Tname,'backgroundcolor','w',...
        'horizon','center','style','edit','call',tname,'visible','off');

    % Other information field
    frame(2) = uicontrol('style','frame','pos',[25 62 420 127],'visible','off','backgroundcolor',[0.8 0.8 0.9]);
    % Call sequences for 4 text fields showing axis limits
    for i = 1:4
        w(i,:) = [
        'sh = get(gcf,''user'');','wind = sh(8:16);'...
            'text = deblank2(get(wind(' num2str(i*2+1) '),''string''));'...
            'sh(' num2str(19+i) ')=str2num(text);','set(wind(' num2str(i*2+1) '),''string'',text);'...
            'set(gcf,''user'',sh);'];
    end
    % Label "Axis limits:"
    wind(1)=uicontrol('style','text','fontweight','bold','backgroundcolor',[0.8 0.8 0.9],...
        'pos',[30 135 410 20],'horizon','left','string','Axis limits:','visible','off');	
    % Label "lower tname = "
    wind(2) = uicontrol('style','text','backgroundcolor',[0.8 0.8 0.9],'pos',[105 132 80 20],...
        'horizon','right','string',['lower ',Tname,' = '],'visible','off');
    % Text field for wind(2)
    wind(3) = uicontrol('style','edit','backgroundcolor','w',...
        'pos',[185 132 50 20],'string',num2str(WINvect(1)),'call',w(1,:),'visible','off');
    % Label "lower x = "
    wind(4) = uicontrol('style','text','backgroundcolor',[0.8 0.8 0.9],...
        'pos',[235 132 125 20],'horizon','right','string',['lower x = '],'visible','off');
    % Text field for wind(4)
    wind(5)=uicontrol('style','edit','backgroundcolor','w',...
        'pos',[185 109 50 20],'string',num2str(WINvect(2)),'call',w(2,:),'visible','off');
    % Label "upper tname = "
    wind(6) = uicontrol('style','text','backgroundcolor',[0.8 0.8 0.9],...
        'pos',[30 109 155 20],'horizon','right','string',['upper ',Tname,' = '],'visible','off');
    % Text field for wind(6)
    wind(7) = uicontrol('style','edit','backgroundcolor','w',...
        'pos',[360 132 50 20],'string',num2str(WINvect(3)),'call',w(3,:),'visible','off');
    % Label "upper x = "
    wind(8) = uicontrol('style','text','backgroundcolor',[0.8 0.8 0.9],...
        'pos',[235 109 125 20],'horizon','right','string',['upper x = '],'visible','off');
    % Text field for wind(8)
    wind(9)=uicontrol('style','edit','backgroundcolor','w',...
        'pos',[360 109 50 20],'string',num2str(WINvect(4)),'call',w(4,:),'visible','off');
    % Label "Overlay on current plot : "
    over_text = uicontrol('style','text','pos',[80 164 155 15],'horizon','center',...
        'string','Overlay on current plot : ','backgroundcolor',[0.8 0.8 0.9],'visible','off');
    % Checkbox for over_text
    ocheck = uicontrol('Style','Checkbox','pos',[230 161 20 20],'Value',1,'backgroundcolor',[0.8 0.8 0.9]);
    % Button "Quit"
    butt(1) = uicontrol('style','push','pos',[82 23 70 20],'fontweight','bold',...
        'string','Quit','call','analyzer(''quit'')','visible','off');
    % Button "Proceed"
    butt(2) = uicontrol('style','push','pos',[317 23 70 20],'fontweight','bold',...
        'string','Proceed','call','analyzer(''proceed'')','visible','off');
    % Button "Close Plots"
    butt(3) = uicontrol('style','push','pos',[200 23 70 20],'fontweight','bold',...
        'string','Close Plots','call','analyzer(''closeplot'')','visible','off');
    % Label "No. of points to be plotted : "
    stepText = uicontrol('style','text','pos',[220 72 150 20],'backgroundcolor',[0.8 0.8 0.9],...
        'string','No. of points to be plotted : ');
    % Default number of points (degree of accuracy)
    noPoints = 100;
    % Call sequence for number of points to be drawn
    no = [
        'sh = get(gcf,''user'');','noPoints = deblank2(get(sh(25),''string''));'...
            'sh(24)=str2num(noPoints);','set(sh(25),''string'',noPoints);'...
            'set(gcf,''user'',sh);'];
    % Text field for stepText
    stepEdit = uicontrol('style','edit','pos',[360 75 50 20],'backgroundcolor','w',...
        'string',num2str(noPoints),'horizon','center','call',no);
    
    % Label "Version number"
    v_name = uicontrol('style','text','pos',[400 300 70 20],'foregroundcolor',[0.4 0.4 0.4],...
        'string','Version 2.0','backgroundcolor',[0.95 0.85 0.75]);

    % Record the handles in the User Data of the Set Up figure.
    sh = [frame,eq,wind,butt,WINvect,noPoints,stepEdit];
    set(gcf,'user',sh);
    set(get(gcf,'child'),'vis','on');
    
    % Record the equation and independent variable in the User Data
    sm = str2mat(Tname,equation);
    set(frame(1),'user',sm);
    
    % Setting up some initial conditions
    newFig = -1; eqStrCur = [];
    noOfPlots = []; eqStrMat = [cellstr('')];
    curFigure = 0; maxPlotNo = 0;
    indepVar = [cellstr('')]; noOfPoints = [];
    
% Proceed sequences
elseif strcmpi(action,'proceed')
    
    % Proceed connects Setup with the Display window.
    sh       = get(gcf,'user');
    sm       = get(sh(1),'user');
    
    % Obtain the current independent variable and equation
    Tname    = deblank(sm(1,:));
    equation = deblank(sm(2,:));
    
    % Checks whether the equation is solvable (checking syntax also)
    findIfEquationGood( Tname, equation );
    
    % Checking whether to overlay on the same plot window
    overlap = get(ocheck,'Value');
    % Obtain the current number of points
    noPoints = sh(24);
    
    % Call sequences for zoom menu in plot window
    zoomCmd1 = ['h = findobj(gcf,''Label'',''Zoom &in'');',...
            'if strcmp(get(h,''checked''),''off'') ','zoom on;',...
            'set(h,''Checked'',''on'');','else zoom off;',...
            'set(h,''Checked'',''off''); end;'];
    zoomCmd2 = ['zoom off;' 'zoom out;' 'h = findobj(gcf,''Label'',''Zoom &in'');',...
            'set(h,''Checked'',''off'');'];
    
    % Setting up the window for the plot to be drawn
    % Drawing the graph on new plot window
    if (overlap == 0 | newFig == -1)
        % Information required for the equations list printed in Command window
        plotCase = 1;
        curFigure = curFigure + 1;
        indepVar(curFigure) = cellstr(Tname);
        noOfPlots(curFigure) = 1;
        noOfPoints = sh(24);
        eqStrCur = cellstr(equation);
        % Plot window properties
        newFig = figure('name',['ANALYZER PLOT No. ' num2str(curFigure)],'numb','off','color',[0.8 0.9 0.9],...
            'CloseRequestFcn',['warndlg(cellstr({''You can only close this plot from'',',...
                '''main interface by clicking ''''Close Plots'''' button''}))'],'MenuBar','none');
        % Customised menu
        f = uimenu('Label','&Menu');
        uimenu(f,'Label','&Copy to clipboard','Callback','print -dbitmap',...
            'Accelerator','C');
        uimenu(f,'Label','&Print...','Callback','printdlg','Accelerator','P');
        uimenu(f,'Label','&Quit ANALYZER','Separator','on','Callback','analyzer(''quit'')','Accelerator','Q');
        uimenu('Label','&Grid on/off','Callback','grid');
        g = uimenu('Label','&Zoom');
        uimenu(g,'Label','Zoom &in','checked','off','callback',zoomCmd1);
        uimenu(g,'Label','Zoom to &original size','callback',zoomCmd2);
    % Overlay the graph on current plot window
    else
        plotCase = 2;
        if (strcmp(strvcat(indepVar(curFigure)),Tname))
            noOfPlots(curFigure) = noOfPlots(curFigure) + 1;
            noOfPoints = [noOfPoints sh(24)];
            newFig = figure(newFig);
            set(newFig,'name',['ANALYZER PLOT No. ' num2str(curFigure)],'numb','off');
            eqStrCur = [eqStrCur ; cellstr(equation)];
        end
    end
    
    tempNo = size(eqStrCur);
    if tempNo(1) > maxPlotNo
        maxPlotNo = tempNo(1);
    end
    
    lineColor = 'bgkrmcy';

    % Convert all the equations into the matrix form of size
    % (row,col) = (number of windows, maximum number of graphs in one window)
    tempSt = eqStrMat; tempNo2 = size(tempSt);
    for i = 1:curFigure
        for j = 1:maxPlotNo
            eqStrMat(i,j) = cellstr('');
        end
    end
    for i = 1:tempNo2(1)
        for j = 1:tempNo2(2)
            eqStrMat(i,j) = tempSt(i,j);
        end
    end
    for i = 1:tempNo(1)
        eqStrMat(curFigure,i) = eqStrCur(i);
    end
    
    % Display all the plotted equations in the Command window
    clc; disp('Analyzer Plotted Equations');
    disp('============================');
    for i = 1:curFigure
        s = ['Plot ' num2str(i) ':  '];
        for j = 1:noOfPlots(i)
            if j == 1 disp([s, 'x',num2str(j),'(',strvcat(indepVar(i)),') = ',strvcat(eqStrMat(i,j))]);
            else disp([blanks(length(s)) 'x',num2str(j),'(',strvcat(indepVar(i)),') = ',strvcat(eqStrMat(i,j))]); end
        end
        disp(sprintf('\r'));
    end
    
    % In the case of overlaying plots, sends an error if any two graphs
    % have different independent variables
    if (plotCase == 2)
        if (~strcmp(strvcat(indepVar(curFigure)),Tname))
            error(sprintf('Independent variables to be drawn on \nthe same plot window must be identical.'));
        end
    end
    
    % Drawing plot onto the dedicated plot window
    plots = []; c_ind = 1; s_ind = 1;
    for ind = 1:tempNo(1)
        t=linspace(sh(20),sh(21),noOfPoints(ind));
        eval( strcat( Tname, '=t;'));
        eqEvalStr = places(strvcat(eqStrMat(curFigure,ind)));
        if s_ind == 1 lineStyle = '-'; s_ind = s_ind+1;
        elseif s_ind == 2 lineStyle = '--'; s_ind = s_ind+1;
        elseif s_ind == 3 lineStyle = 'x-'; s_ind = s_ind+1;
        elseif s_ind == 4 lineStyle = '-.'; s_ind = s_ind+1;
        else lineStyle = '.-'; s_ind = 1; end
        if (strcmp(strvcat(indepVar(curFigure)),Tname))
            plots(ind) = plot(t,eval(strcat(eqEvalStr,'+t-t')),[lineColor(c_ind),lineStyle]); hold on;
        end
        if (s_ind == 1)
            c_ind = c_ind + 1;
            if (c_ind > 7) c_ind = 1; end
        end
    end
    if (strcmp(strvcat(indepVar(curFigure)),Tname))
        axis([sh(20),sh(21),sh(22),sh(23)])
        title(['Output Plot No.' num2str(curFigure)])
        xlabel(Tname); ylabel('x'); lstr = [];
        for i = 1:length(plots)
            lstr = strvcat(lstr,char(eqStrMat(curFigure,i)));
        end
        legend(plots,lstr,0);
    end
    
% Closing plot windows sequences
elseif strcmpi(action,'closeplot')
    % this looks for any opened plot windows and
    % forces to close all found.
    figs = get(0,'children');
    for (figno = 1:length(figs))
        nn = get(figs(figno),'name');
        TTT = findstr(nn,'ANALYZER PLOT No.');
        SSS = findstr(nn,'WARNING!!');
        if (~isempty(TTT)|~isempty(SSS)) delete(figs(figno))
        end
    end
    newFig = -1; eqStrCur = [];
    noOfPlots = []; eqStrMat = [cellstr('')];
    curFigure = 0; maxPlotNo = 0; noOfPoints = [];
    
% Quitting sequences
elseif strcmpi(action,'quit')
    % 'quit' is the callback of the Quit buttons on the ANALYZER Setup and
    % Display windows.  It provides for an orderly exit, deleting all
    % associated windows.
    selection = questdlg(strvcat('This will quit Analyzer and close all the',...
        'corresponding plots, do you wish to continue?'),...
        'Quit Analyzer','Yes','No','Yes');
    if strcmp(selection, 'Yes')
        figs = get(0,'children');
        for (figno = 1:length(figs))
            nn = get(figs(figno),'name');
            TTT = findstr(nn,'ANALYZER');
            SSS = findstr(nn,'WARNING!!');
            if (~isempty(TTT)|~isempty(SSS)) delete(figs(figno))
            end
        end
    end
    
    
end;

% We wish to do this in a separate function to ensure a separate scope 
% which MATLAB will automagically create for us on a function invokation.
% Function algorithm and idea was implemented by Kelsey Grant.
function findIfEquationGood( TName, equation ) 
eval( strcat( TName,'= 0;'));
eval( equation );

% Small function to put in . after the "*","^" and "/"
% in an equation, so it can be solved vector-wise
function t=places(t)
placestimes=find(t=='*'); 
placespower=find(t=='^'); 
placesdiv=find(t=='/');
place=sort([placespower,placesdiv,placestimes]); 
many=length(place);
for i=1:many
   t=[t(1:place(i)-1),'.',t(place(i):length(t))]; 
   place=place+1;
end