function varargout = myplacement(varargin)

global a;
global magp;
global phasep;
global impulsep;
global zplanep;
global placepoles placezeroes newpole showsurface showcookie surfacefig shownormalisedfreq;
global clearpoles donenewpole N;
%evalin('caller','if ~exist(''zeroes'') global zeroes; end;')
evalin('caller','global zeroes;')
global zeroes;
if (isempty(zeroes)) zeroes=[]; end;
%evalin('caller','if ~exist(''poles'') global poles; end;') 
evalin('caller','global poles;') 
global poles;
if (isempty(poles)) poles=[]; end;

if nargin == 0
    action = 'init';
    %    shh = get(0,'ShowHiddenHandles');
    %    set(0,'ShowHiddenHandles','on')
    %    spfig = findobj(0,'Tag','sptool');
    %    set(0,'ShowHiddenHandles',shh);
    %    if ~isempty(spfig)
    %        figure(spfig)
    %        return
    %    end
else
    action = varargin{1};
    eval(action);
end

%[a,magp,phasep,impulsep,zplanep]=placement2;                        

switch action
    
case 'init'
    
    
    % AJL STUFF (GLOBAL FLAGS)
    placepoles = 0; % we are noew playing with pole placement
    placezeroes = 1; % we are now playing with zero placement
    newpole = 0; % used to store a button press location on the zplane
    showsurface = 0; % show the z transform as a surface in separate figure
    showcookie = 0; % show the unit circle only as surface in sepearate figure
    surfacefig = 0; % seperate figure handle for surface drawing
    shownormalisedfreq = 0; % show in the seperate figure the freqz output
    clearpoles = 1; % whether to zero the list
    donenewpole = 0; % a flag
    if ~isempty(poles)	
        clearpoles = 0;
        donenewpole = 1;
    else
        poles = []; % list of current poles
    end;
    if ~isempty(zeroes)
        clearpoles = 0;
        donenewpole = 1;
    else
        zeroes = []; % list of current poles
    end;
    
    N = 128; % number of samples in impulse response
    
    
    [a,magp,phasep,impulsep,zplanep]=placement2;                        

    % Generate a structure of handles to pass to callbacks, and store it. 
	%handles = guihandles(a)
	%guidata(a, handles);
    % AJL now these are the remembered parts of the GUI
 
    % AJL STUFF (MAIN LOOP)
    %axes(zplanep);
    %if findstr(version,'5.2') == 1
    %	  set(zplanep,'Color',[ 0 0 0]);
    %end;
    %axis([-1 1 -1 1]);
    %zgrid;
    %drawnow;
    if clearpoles == 1
        myplacement('clearpoles = 1;'); % recursively call back to get first draw
    else
        myplacement('clearpoles = 0; donenewpole = 1;'); % recursively call back to get first draw
    end;

    
otherwise
 
    %[obj,a] = gcbo;
  %  a = gcbf
    figure(a)
%     handles = guidata(a)
%  	handles2 = guihandles(a)
%     zplanep = handles2.zplane;
%     magp = handles2.mag;
%     phasep = handles2.phase;
%     impulsep = handles2.impulse;

    if clearpoles ~= 0
        disp('Clearing all poles and zeroes');
        clearpoles = 0;
        poles = [];
        zeroes = [];
        
    end;
    
    if newpole ~= 0  
        newpole =0;
        donenewpole = 1;  
        %    disp('Placing a singularity');
        %%%%%    figure(a);
        axes(zplanep);
        
        polelocation = ginput(1)
        
        if placepoles ~= 0
            if polelocation(2) == 0
                poles = [poles; (polelocation(1) + j*0)];
            else
                poles = [poles;  (polelocation(1) + j*polelocation(2))];
                poles = [poles;  (polelocation(1) - j*polelocation(2))];
            end;
        end;
        if placezeroes ~= 0
            if polelocation(2) == 0
                zeroes = [zeroes; (polelocation(1) +j*0)];
            else
                zeroes = [zeroes; (polelocation(1) + j*polelocation(2))];
                zeroes = [zeroes; (polelocation(1) - j*polelocation(2))];
            end;
        end;
    end;
    
    % work out the impulse response
    theimpulseresponse = zeros(1,N);
    theimpulseresponse(1) = 1;
    numerator = poly(zeroes);
    denominator = poly(poles);
    theimpulseresponse=filter(numerator,denominator,theimpulseresponse);
    
    hold off;
    axes(zplanep);
    %hold off;
    %cla;
    if findstr(version,'5.2') ~= []
        set(zplanep,'Color',[ 0 0 0]);
    end;
    cla;
    hold off
    zgrid;
    hold on
    %pzmap(poles,zeroes);
    if poles ~= []
        plot(poles,'*r')
    end
    hold on;
    if zeroes ~= []
        plot(zeroes,'og')
    end
    
    axis([-1 1 -1 1]);
    hold off;
    axes(magp);
    dft = fft(theimpulseresponse);
    plot(abs(dft));
    axes(phasep);
   plot(angle(dft));
    axes(impulsep);
   plot(theimpulseresponse);
    drawnow;
   axes(zplanep);
    
    if showsurface ~= 0
        showsurface = 0;
        if surfacefig ~= 0 
            figure(surfacefig);
        else
            surfacefig = figure;
        end;
        rationaltransformplot(poles,zeroes,2,'log');
        drawnow;%figure(a)
    elseif showcookie ~= 0
        showcookie = 0;
        if surfacefig ~= 0 
            figure(surfacefig)
        else
            surfacefig = figure;
        end;
        rationaltransformplot(poles,zeroes,2,'zringonly');
        drawnow;%figure(a)
    elseif ((shownormalisedfreq ~= 0)&(donenewpole ~=0))
        donenewpole = 0;
        if surfacefig ~= 0 
            figure(surfacefig)
        else
            surfacefig = figure;
        end;
        freqz(numerator,denominator);
        drawnow;
        %figure(a);
    end;
    
end; %switch