function output = dfield(action,input1,input2,input3)

% DFIELD	is an interactive tool for studying single first order
%	differential equations.  When DFIELD is executed, a DFIELD Setup
%	window is opened.  The user may enter the differential
%	equation and specify a display window using the interactive
%	controls in the Setup window.
%
%	When the Proceed button is pressed on the Setup window, the DF
%	Display window is opened.  At first this window displays a
%	direction line field for the differential equation.  When the
%	mouse button is depressed in the DFIELD Display window, the
%	solution to the differential equation with that initial
%	condition is calculated and plotted.
%
%	Other options are available in the Options menu.  These are
%	fairly self explanatory.  The Settings option allows the user
%	to change several parameters.  Included here are the
%	possibilities of using a vector field instead of the default
%	line field, and of changing the number of field points computed
%	and displayed.

%  Copywright (c) 1993 - 95 by John C. Polking, Rice University
%  Last modified:  January 30, 1995

if nargin <1
	action ='initialize';
end


if strcmp(action,'initialize')

	% First we make sure that there is no other copy of DFIELD
	% running, since this causes problems.

	figs = get(0,'children');
	for (figno = 1:length(figs))
		nn = get(figs(figno),'name');
		if (length(nn) >1)
			if (findstr(nn,'DFIELD')~=[])
				error('Only one copy of DFIELD can be open at one time.')
			end
		end
	end

	% Initiate several parameters.

	NumbFPts = 20;	% The number of field points plotted in each direction.
	Arrflag=1;		% The default is a vector field.
	magn = 1.25;		% The expansion factor in each direction 
				% for the compute window.
	steps = 20;		% Then minimum number of compute stepss across 
				% the Display window.
	tol = 1e-4;		% The relative error tolerance.
	itlim = 1000;		% After this many iterations, the computation of 
				% a solution stops.
	settings = [Arrflag,NumbFPts,magn,steps,itlim,tol];

	% The default differential equation, and Display window.

	Xname = ' x';
	Tname = ' t';
	derivstr = ' x^2 - t';
	WINvect=[-3 10 -4 4];

	% Build the Setup window.
	
	texth =20;   		% Height of text boxes.
	varw = 80;		% Length of variable boxes.
	equalw =30;		% Length of equals.
	eqlength = 300;		% Length of right hand sides.
	left =30;		% Left margin.
	
	separation = texth+3;	% Separation between boxes.
	equationbot = 7.5*separation;;
	eqlabelbot = equationbot + 2.5*separation;
	xbot = equationbot + 1.5*separation;	% Bottom of x equation.
	tbot = equationbot;			% Bottom of t equation.
	
	defigwidth =2*left + varw+equalw+eqlength;	% Width of the figure.
	defigureheight = 12*separation;			% Height of the figure.
	defigurebot = 20;				% Bottom of the figure.
	
	dfset = figure('pos',[20 defigurebot defigwidth defigureheight],...
		'resize','off','name','DFIELD Setup','numb','off',...
		'visible','off');
	figure(dfset)

	lablen =160;
	
	eqlableft = (defigwidth-lablen)/2;
	
	frame(1) = uicontrol('style','frame',...
		'pos',[left-5,equationbot-5,defigwidth-2*left+10,3.5*separation+10],...
		'visible','off');

	tname = [
	'sh = get(gcf,''user'');'...
	'sm = get(sh(1),''user'');'...
	'eq = sh(3:8);'...
	'wind =sh(9:17);'...
	'Tname=get(eq(6),''string'');'...
	'set(wind(2),''string'',[''The min value of '',Tname,'' = '']);'...
	'set(wind(4),''string'',[''The max value of '',Tname,'' = '']);'...
	'sm = str2mat(Tname,sm(2:3,:));'...
	'set(sh(1),''user'',sm);'...
	'set(sh(3),''user'',0);']; 	% Set's the flag to compute anew.

	xname=[
	'sh = get(gcf,''user'');'...
	'sm = get(sh(1),''user'');'...
	'eq = sh(3:8);'...
	'wind =sh(9:17);'...
	'Xname=get(eq(2),''string'');'...
	'set(wind(6),''string'',[''The min value of '',Xname,'' = '']);'...
	'set(wind(8),''string'',[''The max value of '',Xname,'' = '']);'...
	'sm = str2mat(sm(1,:),Xname,sm(3,:));'...
	'set(sh(1),''user'',sm);'...
	'set(sh(3),''user'',0);'];

	xder =[
	'sh = get(gcf,''user'');'...
	'sm = get(sh(1),''user'');'...
	'eq=sh(3:8);'...
	'derivstr = get(eq(4),''string'');'...
	'sm = str2mat(sm(1:2,:),derivstr);'...
	'set(sh(1),''user'',sm);'...
	'set(sh(3),''user'',0);'];


	eq(1)=uicontrol('style','text',...
		'pos',[left eqlabelbot defigwidth-2*left texth],...
		'horizon','center',...
		'string','The differential equation.','visible','off');
	
	eq(2)=uicontrol('pos',[left xbot varw texth],'style','edit',...
		'horizon','right','string',Xname,...
		'call',xname,'visible','off');
	
	eq(3) = uicontrol('style','text','pos',[left+varw xbot equalw texth],...
		'horizon','center','string',''' = ','visible','off');
		
	eq(4)=uicontrol('pos',[left+varw + equalw xbot eqlength texth],...
		'string',derivstr,'horizon','left','style','edit',...
		'call',xder,'visible','off');
		
	eq(5)=uicontrol('pos',[left tbot 200 texth],'style','text',...
		'horizon','right','string','The independent variable is ',...
		'visible','off');
			
	eq(6)=uicontrol('pos',[left+200 tbot varw texth],...
		'string',Tname,...
		'horizon','right','style','edit','call',tname,...
		'visible','off');
	
	winstrlen = (defigwidth - 2*left)/2 -50;
	winbot = 2*separation;
	winleft = left+(winstrlen +50 -120)/2;
	wframe=[left-5,winbot+separation-5,...
		defigwidth-2*left+10,3*separation+10];
		
	w1 = [
	'sh = get(gcf,''user'');'...
	'wind =sh(9:17);'...
	'sh(21)=str2num(get(wind(3),''string''));'...
	'set(gcf,''user'',sh);'];
	
	w2 = [
	'sh = get(gcf,''user'');'...
	'wind =sh(9:17);'...
	'sh(22)=str2num(get(wind(5),''string''));'...
	'set(gcf,''user'',sh);'];
	
	w3 = [
	'sh = get(gcf,''user'');'...
	'wind =sh(9:17);'...
	'sh(23)=str2num(get(wind(7),''string''));'...
	'set(gcf,''user'',sh);'];


	w4 = [
	'sh = get(gcf,''user'');'...
	'wind =sh(9:17);'...
	'sh(24)=str2num(get(wind(9),''string''));'...
	'set(gcf,''user'',sh);'];

	
	frame(2) = uicontrol('style','frame','pos',wframe,'visible','off');
	
	wind(1)=uicontrol('style','text',...
		'pos',[left winbot+3*separation defigwidth - 2*left texth],...
		'horizon','center','string','The display window.','visible','off');
		
	wind(2) = uicontrol('style','text',...
		'pos',[left winbot+2*separation winstrlen texth],...
		'horizon','right','string',['The min value of ',Tname,' = '],...
		'visible','off');

	wind(3) = uicontrol('style','edit',...
		'pos',[left+winstrlen winbot+2*separation 50 texth],...
		'string',num2str(WINvect(1)),...
		'call',w1,'visible','off');
	
	wind(4) = uicontrol('style','text',...
		'pos',[left winbot+separation winstrlen texth],...
		'horizon','right','string',['The max value of ',Tname,' = '],...
		'visible','off');
	
	wind(5) = uicontrol('style','edit',...
		'pos',[left+winstrlen winbot+separation 50 texth],...
		'string',num2str(WINvect(2)),...
		'call',w2,'visible','off');
		
	wind(6) = uicontrol('style','text',...
		'pos',[left+winstrlen+50 winbot+2*separation winstrlen texth],...
		'horizon','right','string',['The min value of ',Xname,' = '],...
		'visible','off');

	wind(7) = uicontrol('style','edit',...
		'pos',[left+2*winstrlen+50 winbot+2*separation 50 texth],...
		'string',num2str(WINvect(3)),...
		'call',w3,'visible','off');
	
	wind(8) = uicontrol('style','text',...
		'pos',[left+winstrlen+50 winbot+separation winstrlen texth],...
		'horizon','right','string',['The max value of ',Xname,' = '],...
		'visible','off');
		
	wind(9) = uicontrol('style','edit',...
		'pos',[left+2*winstrlen+50 winbot+separation 50 texth],...
		'string',num2str(WINvect(4)),...
		'call',w4,'visible','off');
		
	butt(1) = uicontrol('style','push',...
		'pos',[(defigwidth/4-35),separation,70,texth],...
		'string','Quit','call','dfield(''quit'')','visible','off');
	
	butt(2) = uicontrol('style','push',...
		'pos',[(defigwidth/2-35),separation,70,texth],...
		'string','Revert','call','dfield(''revert'')','visible','off');
		
	butt(3) = uicontrol('style','push',...
		'pos',[(3*defigwidth/4-35),separation,70,texth],...
		'string','Proceed','call','dfield(''proceed'')','visible','off');
		
% Record the handles in the User Data of the Set Up figure.
		
	sh = [frame,eq,wind,butt,WINvect,WINvect,settings];
	set(gcf,'user',sh);
	set(gcf,'pos',[20 defigurebot defigwidth defigureheight],'vis','on');
	set(get(gcf,'child'),'vis','on');
	
% Record the important information in the User Data of
% varous controls.  

	sm = str2mat(Tname,Xname,derivstr);
	set(frame(1),'user',sm);
	set(frame(2),'user',sm);	%  This is long term memory.
	set(sh(3),'user',0);
		

elseif strcmp(action,'proceed')

% Proceed connects Setup with the Display window.

	dfset = gcf;
	sh = get(dfset,'user');
	flag = get (sh(3),'user'); 	

	%  flag = 0, if this is the first time through for this equation, 
	%  but flag = 1 if only the window dimensions have been changed.

	if (flag == 1)
		WINvect = sh(21:24);
		sh(25:28) = WINvect;
		set(dfset,'user',sh);	
		dfdisp = 0;
		figs = get(0,'children');
		for (kk = 1:length(figs))
			if (strcmp(get(figs(kk),'name'),'DFIELD Display'))
				dfdisp = figs(kk);
			end
		end
		dh = get(dfdisp,'user');
		dh(15:18) = WINvect;
		set(dfdisp,'user',dh);
		dfield('dirfield');
	else
		set(sh(3),'user',1);
		set(dfset,'user',sh);	
		dfield('display');
	end	

			
elseif strcmp(action,'revert')

% Revert allows the user to change all settings in theSetup window to
% what they were before changes have been made.

	sh = get(gcf,'user');
	frame=sh(1:2);
	eq=sh(3:8);
	wind =sh(9:17);
	sm = get(sh(2),'user');
	Tname = deblank(sm(1,:));
	Xname = deblank(sm(2,:));
	derivstr = deblank(sm(3,:));
	WINvect = sh(25:28);

	set(sh(1),'user',sm);
	
	set(eq(2),'string',Xname);
	set(wind(2),'string',['The min value of ',Tname,' = ']);
	set(wind(4),'string',['The max value of ',Tname,' = ']);
	set(eq(6),'string',Tname);
	set(wind(6),'string',['The min value of ',Xname,' = ']);
	set(wind(8),'string',['The max value of ',Xname,' = ']);
	set(eq(4),'string',derivstr);
	set(wind(3),'string',num2str(WINvect(1)));
	set(wind(5),'string',num2str(WINvect(2)));
	set(wind(7),'string',num2str(WINvect(3)));
	set(wind(9),'string',num2str(WINvect(4)));
	sh(21:24) = WINvect;
	set(gcf,'user',sh);

elseif strcmp(action,'display')

% Display takes the information from the Setup window and initializes
% the Display window if it already exists.  If the Display window does
% not exist, it builds one.
	
	dfset = gcf;

% Find DFIELD Display if it exists.
	
	figs = get(0,'children');
	dfdisp = 0;
	for (figno = 1:length(figs))
		if (strcmp(get(figs(figno),'name'),'DFIELD Display'))
			dfdisp = figs(figno);
			figure(dfdisp);
			dh = get(dfdisp,'user');
			dfdispa = dh(14);
			axes(dfdispa);
			cla
			notice = dh(2:3);
			set(notice(1),'string','Computing the field elements.');
			set(notice(2),'string','');
		end
	end

% Get the information from DFIELD Setup.

	sh = get(dfset,'user');
	settings = sh(29:34);
	WINvect = sh(21:24);
	
	sm = get(sh(1),'user');
	set(sh(2),'user',sm);	% Resets long term storage.
	
	Tname = deblank(sm(1,:));
	Xname = deblank(sm(2,:));
	derivstr = deblank(sm(3,:));
	Labstr = [Xname,''' = ',derivstr];
	sh(25:28) = WINvect;
	set(gcf,'user',sh);

% If DFIELD Display exists, update it.  If it does not build it.
		
	if (dfdisp)
		dh(15:18) = WINvect;
		set(dfdisp,'user',dh);
		dm = get(dh(1),'user');
		FFFCCNNN = deblank(dm(3,:));
		dm = str2mat(Tname,Xname,FFFCCNNN,Labstr);
		set(dh(1),'user',dm);
	else
		dfdisp = figure('name','DFIELD Display','numb','off',...
			'visible','off');
		figure(dfdisp);
		Arrflag = settings(1);
		
		% Set up the bulletin window.
		
		nframe = uicontrol('style','frame','units','normal',...
			'pos',[.1 0 .78 .09],'visible','off');
		
		notice(1)=uicontrol('style','text','pos',[.12 .045 .74 .04],...
			'units','normal','horiz','left',...
			'string','Computing the field elements.','visible','off');
		
		notice(2)=uicontrol('style','text','pos',[.12 .005 .74 .04],...
			'units','normal','horiz','left','string','',...
			'visible','off');
		
%		drawnow
		
		% Set up the buttons and the menu.

		dbutt(1) = uicontrol('style','push','units','normal','pos',...
			[0.895 0.17 0.09 0.06],'string','Quit',...
			'call','dfield(''quit'')','visible','off');
		
		dbutt(2) = uicontrol('style','push','units','normal','pos',...
			[0.895 0.86 0.09 0.06],'string','Replot','call',...
			'dfield(''refresh'')','visible','off','value',1);

		dbutt(3) = uicontrol('style','push','units','normal','pos',...
			[0.895 0.515 0.09 0.06],'string','Print',...
			'call','dfield(''print'')','visible','off');

		v = version;
		if (findstr('tudent', v))
			v = 4.2;
		else
			v = str2num(v(1:3));
		end

		dbutt(4) = v;
			
		menu(1) = uimenu('label','DFIELD Options','visible','off');

		menukey = uimenu(menu(1),'label','Keyboard input.','call',...
			'dfield(''kbd'')');

		mesev   = uimenu(menu(1),'label','Plot several solutions.',...
			'call','dfield(''several'')');

		menu(2) = uimenu(menu(1),'label','Zoom in.','call',...
			'dfield(''zoomin'')','separator','on');

		menu(4) = uimenu(menu(1),'label','Erase all solutions.',...
			'call','dfield(''dall'')','separator','on');

		menu(5)   = uimenu(menu(1),'label','Delete a graphics object.',...
			'call','dfield(''delete'')');

		menutext = uimenu(menu(1),'label','Enter text on the Display Window.',...
			'call','dfield(''text'')');

		meset = uimenu(menu(1),'label','Settings.',...
			'call','dfield(''settings'')','separator','on');

		menu(6) = uimenu(menu(1),'label','Make the Display Window inactive.',...
			'call','dfield(''hotcold'')','separator','on');
		
		if (v > 4.0)
			menu(3)   = uimenu(menu(1),'label','Replot solutions later.',...
			'call','dfield(''replot'')','separator','on');
		else
			menu(3) = 0;
		end

		set(dfdisp,'visible','on');
		set([nframe, notice, dbutt([1 3]),menu(1)],'visible','on');
%		if (dbutt(4) < 4.1) 
%			set(menu(3),'visible','off'); 
%		end
		drawnow	
		dfdispa=axes('position',[.1 .17 .78 .75],...
			'next','add','box','on',...
			'xgrid','on','ygrid','on');

		set(gcf,'WindowButtonDownFcn','dfield(''down'')');
	
	% Save the numbers:
	
		% dh(1)			nframe
		% dh(2:3)		notice
		% dh(4:7)		dbutt  (dbutt(4) = version of MATLAB)
		% dh(8:13)		menu
		% dh(14)		ddispa
		% dh(15:18)		WINvect
		% dh(19:24)		settings
		% dh(25)		RFLAG
	
		dh = [nframe,notice,dbutt,menu,dfdispa,WINvect,settings];
		set(dfdisp,'user',dh);

		
		dm = str2mat(Tname,Xname,' ',Labstr);
		set(dh(1),'user',dm);
		
	end
		
	
% We have to make the derivative string array smart.
	
	l = length(derivstr);
	for (k=fliplr(find((derivstr=='^')|(derivstr=='*')|(derivstr=='/'))))
		derivstr = [derivstr(1:k-1) '.' derivstr(k:l)];
		l = l+1;
	end
	
% If an old function m-file exists delete it, and then build a new one.
	
	if (exist(FFFCCNNN)==2) delete([FFFCCNNN,'.m']);end
	tee = clock;
	tee = ceil(tee(6)*100);
	FFFCCNNN=['dftp',num2str(tee)];
	
	fcnstr = ['function YyYypr = ',FFFCCNNN,'(TtTt,YyYy)\n\n'];
	varstr = [Tname,' = TtTt;', Xname,' = YyYy;\n\n'];
	lenstr = ['l = length(YyYy);\n'];
	derstr1 = ['YyYypr = ', derivstr,';\n'];
	derstr2 = ['if (length(YyYypr) < l) YyYypr = YyYypr*ones(1,l);end\n'];
	
	dff = fopen([FFFCCNNN,'.m'],'w');
	fprintf(dff,fcnstr);
	fprintf(dff,varstr);
	fprintf(dff,lenstr);
	fprintf(dff,derstr1);
	fprintf(dff,derstr2);
	fclose(dff);

% Initialize important information as user data.
	
	dm = str2mat(dm(1:2,:),FFFCCNNN,dm(4,:));
	set(dh(1),'user',dm);	% The strings.
	set(dh(3),'user',[]);	% Handles to solution curves.
	set(dh(8),'user',[]);	% Data for solution curves which are 
				% still plotted with no erase mode, 
				% and must be replotted at some point.
	set(dh(12),'user',[]);	% Handles for the direction and vector fields.
	set(dfdispa,'user',[]);	% Handles for the ends of orbits plotted with 
				% no erasemode.  These must be deleted at 
				% some point.
	dfield('dirfield');	

elseif strcmp(action,'replot')

% This is the callback for the Replot button.  This is only visible if
% the version of MATLAB is 4.1 or greater.  In this case "enable" is
% defined, so we need not check further.

	dh = get(gcf,'user');
	menu = dh(8:13);
	dbutt = dh(4:7);
	RFLAG = strcmp(get(menu(3),'label'),'Replot solutions immediately.');
	set(dh(5),'value',RFLAG);
	if RFLAG
		set(menu(3),'label','Replot solutions later.');
		set(dbutt(2),'visible','off');
	else
		set(menu(3),'label','Replot solutions immediately.');
		set(dbutt(2),'visible','on');
	end
	dfield('refresh');


elseif strcmp(action,'hotcold')

% 'hotcold' is the callback for the menu selection that makes the
% Display Window active or inactive.

	dfdisp = gcf;
	dh = get(dfdisp,'user');
	notice = dh(2:3);
	mehc = dh(13);
	if (findstr(get(mehc,'label'),'inactive'))
		set(dfdisp,'WindowButtonDownFcn',' ');
		set(mehc,'label','Make the Display Window active.');
		set(notice(1),'string','The Display Window is not active.');
		set(notice(2),'string',' ');
	else
		set(dfdisp,'WindowButtonDownFcn','dfield(''down'')');
		set(mehc,'label','Make the Display Window inactive.');
		set(notice(1),'string','Ready.');
		set(notice(2),'string',' ');
	end
	dfield('refresh');



elseif strcmp(action,'dirfield')

% 'dirfield' computes and plots the field elements.  This is the entry
% point both from 'display' and from later commands that require the
% recomputation of the field elements.
	
	% Find DFIELD Display and get the user data.

	figs = get(0,'children');
	dfdisp = 0;
	for (figno = 1:length(figs))
		if (strcmp(get(figs(figno),'name'),'DFIELD Display'))
			dfdisp = figs(figno);
		end
	end

	dh = get(dfdisp,'user');
	dm = get(dh(1),'user');
	Tname = deblank(dm(1,:));
	Xname = deblank(dm(2,:));
	FFFCCNNN = deblank(dm(3,:));
	Labstr = deblank(dm(4,:));
	notice = dh(2:3);
	dfdispa = dh(14);
	WINvect = dh(15:18);
	settings = dh(19:24);
	set(notice(1),'string','Computing the field elements.');
	set(notice(2),'string','');

	Tmin = WINvect(1);
	Tmax = WINvect(2);
	Xmin = WINvect(3);
	Xmax = WINvect(4);
	
	N = settings(2);
	deltat=(Tmax - Tmin)/(N-1);
	deltax=(Xmax - Xmin)/(N-1);
	
	% Set up the display window.
	
	Dtint=[Tmin-deltat,Tmax+deltat];
	Dxint=[Xmin-deltax,Xmax+deltax];
	
	% Set up the original mesh.
	
	TTTg=Tmin + deltat*[0:N-1];
	XXXg=Xmin + deltax*[0:N-1];
	
	[Tt,Xx]=meshgrid(TTTg,XXXg);
		
	% Calculate the line and vector fields.

	Xx=Xx(:);Tt=Tt(:);
	Ww = feval(FFFCCNNN,Tt',Xx');
	Vv = ones(size(Ww)) + Ww*sqrt(-1);
	Vv = Vv.';

	set(notice(1),'string','Computing the graphic elements.');
	set(notice(2),'string','');
	
	Arrflag = settings(1);
	N = settings(2);
	deltat = (WINvect(2) - WINvect(1))/(N-1);
	deltax = (WINvect(4) - WINvect(3))/(N-1);
	
	mgrid = Tt+Xx.*sqrt(-1); % mgrid = mgrid(:);
	zz=Vv.';
	sc = min(deltat,deltax);

	arrow=[-1,1].';
	zzz=sign(zz);
	scale = sqrt((real(zzz)/deltat).^2+(imag(zzz)/deltax).^2);
	ww = (zzz == 0);
	scale = scale + ww;
	aa1 = 0.3*arrow*(zzz./scale)+ones(size(arrow))*(mgrid.');
	[r,c] = size(aa1);
	aa1 = [aa1;NaN*ones(1,c)];
	aa1 = aa1(:);

	arrow = [0,1,.7,1,.7].' + [0,0,.25,0,-.25].' * sqrt(-1);
	zz=sign(zz).*((abs(zz)).^(1/3));
	scale = 0.9*sc./max(max(abs(zz)));
	aa2 = scale*arrow*zz +ones(size(arrow))*(mgrid.');
	[r,c] = size(aa2);
	aa2 = [aa2;NaN*ones(1,c)];
	aa2 = aa2(:);
	axes(dfdispa);

	arrh = get(dh(12),'user');	% Delete the old field data.
	if (arrh ~= [])
		delete(arrh);
	end

	% We plot both the line field and the vector field.  Then we
	% control which is seen by manipulating the visibility.

	if (Arrflag ==1)
		arrh(1) = plot(real(aa1),imag(aa1),'-c','visible','on');
		arrh(2) = plot(real(aa2),imag(aa2),'-c','visible','off');
	elseif (Arrflag == 2)
		arrh(1) = plot(real(aa1),imag(aa1),'-c','visible','off');
		arrh(2) = plot(real(aa2),imag(aa2),'-c','visible','on');
	else
		arrh(1) = plot(real(aa1),imag(aa1),'-c','visible','off');
		arrh(2) = plot(real(aa2),imag(aa2),'-c','visible','off');
	end
	set(dh(12),'user',arrh);	% Save the handles for later use.
		

	title(Labstr);
	xlabel(Tname);ylabel(Xname);

	set(notice(1),'string','Ready.');
	set(notice(2),'string','');
	axis([Dtint,Dxint]);
	dfield('refresh');
	

elseif strcmp(action,'down')

% 'down' is the Window Button Down call.  It starts the computation of
% solutions from a click of the mouse.

	dh = get(gcf,'user');
	notice = dh(2:3);
	initpt = get(gca,'currentpoint');
	initpt = initpt(1,[1,2]);
	dfield('solution',initpt);
	RFLAG = get(dh(5),'value');
	if RFLAG
		dfield('refresh');
	end
	set(notice(1),'string','Ready.')
	set(notice(2),'string',' ');
	

elseif strcmp(action,'several')

% 'several' allows the user to pick several initial points at once.
% This is not needed in X-windows, but it is on the Macintosh.

	dh = get(gcf,'user');
	notice = dh(2:3);
	RFLAG = get(dh(5),'value');
	set(notice(1),'string','Pick initial points with the mouse.')
	set(notice(2),'string','Enter "Return" when finished.');
	[X,Y]=ginput;
	NN = length(X);
	set(notice(1),'string','Working.')
	set(notice(2),'string','');
	for k = 1:NN
		initpt = [X(k),Y(k)];
		dfield('solution',initpt);
	end
	if RFLAG
		dfield('refresh')
	end
	set(notice(1),'string','Ready.')
	set(notice(2),'string',' ');
	
elseif strcmp(action,'solution')

% 'solution' affects the computation and (erasemode == none) plotting of
% solutions.  It also stores the data as appropriate.

	dh = get(gcf,'user');
	dm = get(dh(1),'user');
	notice = dh(2:3);
	RFLAG = get(dh(5),'value');
	if (RFLAG == 0)
		if (strcmp(get(dh(5),'enable'),'off'))
			set(dh(5),'enable','on'); 
		end
	end

	initpt = input1;
	FFFCCNNN = deblank(dm(3,:));;
	dfdispa = dh(14);
	settings = dh(19:24);
	
	ptstr = [' (',num2str(initpt(1)), ', ', num2str(initpt(2)), ').'];

	set(notice(1),'string',...
		['Working on the forward trajectory from',ptstr])
					
	Dxint = get(dfdispa,'xlim');
	Dyint = get(dfdispa,'ylim');
	htemp = get(dfdispa,'user');
	
	window = [Dxint, Dyint];
	magn = settings(3);
	steps = settings(4);
	itlim = settings(5);
	tol = settings(6);
	
	[tp,xp] = dfsolve(FFFCCNNN,initpt,window,magn,1.0,steps,tol,itlim); 
	hnew = get(dfdispa,'children');
	hnew = hnew(1);
	htemp = [htemp;hnew];	% Save the handles of the orbit ends.

	
	set(notice(1),'string',...
		['Working on the backward trajectory from',ptstr])
	
	[tm,xm] = dfsolve(FFFCCNNN,initpt,window,magn,-1.0,steps,tol,itlim);
	hnew = get(dfdispa,'children');
	hnew = hnew(1);
	htemp = [htemp;hnew];	% Save the handles of the orbit ends.

	
	% Store the trajectory.
	
	xm = flipud([tm,xm]);
	x=[xm;[tp,xp]];
	
	newtraj = get(dh(8),'user');
	[mm,nn] = size(newtraj);
	if (nn == 0)
		newtraj = x;
	else
		% In this case we have to make sure the 
		% trajectories fit in the same matrix.
		l = size(x,1);
		if (l < mm)
			x=[x;ones(mm-l,1)*x(l,:)];
		elseif (mm < l)
			newtraj = [newtraj;ones(l-mm,1)*newtraj(mm,:)];
		end
		newtraj=[newtraj,x];
	end
	set(dh(8),'user',newtraj);
	set(notice(2),'string','Ready.');
	set(dfdispa,'user',htemp);	% Save the handles of the orbit ends.


elseif strcmp(action,'kcompute')

% 'kcompute' is the call back for the Compute button on the DFIELD Keyboard figure.

	errmsg1 = 'Enter initial values for both variables.';
	errmsg2 = 'You must start DFIELD from the beginning.';
	kh = get(gcf,'user');
	initpt = [str2num(get(kh(2),'string')),str2num(get(kh(4),'string'))];
	if (length(initpt) ~= 2)
		error(errmsg1);
	end
	figs = get(0,'children');
	dfdisp = 0;
	for (figno = 1:length(figs));
		if (strcmp(get(figs(figno),'name'),'DFIELD Display'))
			dfdisp = figs(figno);
		end
	end
	if (dfdisp == 0)
		error(errmsg2);
	else
		figure(dfdisp);
		dfield('solution',initpt);
		dh = get(dfdisp,'user');
		notice = dh(2:3);
		RFLAG = get(dh(5),'value');
		if RFLAG
			dfield('refresh');
		end
		set(notice(1),'string','Ready.');
		set(notice(2),'string','');
	end

	
elseif strcmp(action,'kbd')

% 'kbd' is the callback for the Keyboard Input menu selection.  It 
% sets up the DFIELD Keyboard figure which allows accurate input of 
% initial values using the keyboard.

	dh = get(gcf,'user');
	dm = get(dh(1),'user');
	Tname = deblank(dm(1,:));
	Xname = deblank(dm(2,:));

	txtl = 200;txth = 22;
	
	dfkbd = figure('pos',[30 200 (txtl+102) (9*txth)],...
		'resize','off','name','DFIELD Keyboard input','numb','off');
	figure(dfkbd)
	
	
	KBD(1) = uicontrol('style','text','pos',[1 7*txth txtl txth],...
		'horiz','right','string',['The initial value of ',Tname,' = ']);
		
	KBD(2) = uicontrol('style','edit','pos',[txtl+1 7*txth 100 txth],...
		'string','','call','');
		
	KBD(3) = uicontrol('style','text','pos',[1 5*txth txtl txth],...
		'horiz','right',...
		'string',['The initial value of ',Xname,' = ']);
		
	KBD(4) = uicontrol('style','edit','pos',[txtl+1 5*txth 100 txth],...
		'string','');
		
	KBD(5) = uicontrol('style','push',...
		'pos',[(txtl+102)/2-35 3*txth 70 txth],...
		'string','Compute','call','dfield(''kcompute'')');

	KBD(6) = uicontrol('style','push',...
		'pos',[(txtl+102)/2-35,txth,70,txth],...
		'string','Close','call','close');
		
	set(dfkbd,'user',KBD);

		
elseif strcmp(action,'zoomin')

% 'zoomin' is the callback for the Zoomin menu item.  It allows the
% user to pick a new display rectangle by clicking and dragging the mouse.


%
% This codes works with RBBOX.  Until they get it working on the Macintosh 
% we will replace it by the older code.
%
%	set(gcf,'WindowButtonDownFcn','dfield(''zoom'')',...
%		'WindowButtonUpFcn','1;','inter','yes');
%	set(gca,'inter','yes');
%	dh = get(gcf,'user');
%	notice = dh(2:3);
%
%	set(notice(1),'string','Pick a new display rectangle by dragging the mouse.');
%	set(notice(2),'string','');
%
%elseif strcmp(action,'zoom')
%
%	dh = get(gcf,'user');
%	notice = dh(2:3);
%	q1 = get(gcf,'currentpoint');
%	p1 = get(gca,'currentpoint');
%	rbbox([q1 0 0],q1);
%	p2 = get(gca,'currentpoint');
%	a = [p1(1,1:2);p2(1,1:2)];
%	a = [min(a);max(a)];a=a(:);
%	WINvect = a';
%
% The following code is the old code.  To be replaced by the above 
% when RBBOX works.
%
	set(gcf,'WindowButtonDownFcn','');
	dh = get(gcf,'user');
	notice = dh(2:3);

	set(notice(1),'string','Pick out two opposite corners with the mouse.');
	set(notice(2),'string','');
	[x1,y1]=ginput(2);
	WINvect = [min(x1), max(x1), min(y1), max(y1)];

% The following code is valid in both cases.

	dh(15:18) = WINvect;
	set(gcf,'user',dh);
	figure(gcf);
	axes(gca);
	set(gcf,'WindowButtonDownFcn','dfield(''down'')',...
		'WindowButtonUpFcn','');
	dfield('dirfield');
	dfset = 0;
	figs = get(0,'children');
	for ( figno = 1:length(figs) )
		if(strcmp(get(figs(figno),'name'),'DFIELD Setup'))
			dfset = figs(figno);
		end
	end
	if (dfset)
		sh = get(dfset,'user');
		wind = sh(9:17);
		set(wind(3),'string',num2str(WINvect(1)));
		set(wind(5),'string',num2str(WINvect(2)));
		set(wind(7),'string',num2str(WINvect(3)));
		set(wind(9),'string',num2str(WINvect(4)));
		sh(21:24) = WINvect;
		sh(25:28) = WINvect;
		set(dfset,'user',sh);
	end
	
elseif strcmp(action,'dall')

% 'dall' is the callback for the Erase all solutions option.  

	dh = get(gcf,'user');
	notice = dh(2:3);
	set(notice(1),'string','Erasing all trajectories.');
	set(notice(2),'string','');

	dfdispa = dh(14);
	newtraj = get(dh(8),'user');
	trajh = get(dh(3),'user');
	axes(dfdispa);
	htemp = get(dfdispa,'user');
	if (htemp~=[])
		set(htemp,'erase','normal');
		delete(htemp);			% This deletes the orbit ends.
	end
	set(dfdispa,'user',[]);
	delete(trajh);
	set(dh(3),'user',[]);
	set(dh(8),'user',[]);
	if (dh(7) > 4.0)
		set(dh(5),'enable','off');
	end
%	set(dh(5),'visible','off');

	set(notice(1),'string','Ready.');
	set(notice(2),'string','');
	
		
elseif strcmp(action,'settings')

% 'settings' is the call back for the Settings menu option.  It sets
% up the DFIELD Settings window, which allows the user to interactively
% change several parameters that govern the behaviour of the program.
	
	dh = get(gcf,'user');
	settings = dh(19:24);
	Arrflag = settings(1);
	rval1 = ~(Arrflag -1);
	rval2 = (~(Arrflag -2))*2;
	rval3 = (~(Arrflag -3))*3;

	txtl = 350;txth = 18;
	figwidth = txtl+104;
	pbwidth = 80;
	framewidth = 3*pbwidth+2*8+2*10;
	frleft = (figwidth - framewidth)/2;
	frbot = 13*txth-5;
	frpos = [frleft frbot framewidth (txth+10)];
	
	dfsettings = figure('pos',[150 50 figwidth (15*txth)],...
		'resize','off','name','DFIELD Settings','numb','off');
	figure(dfsettings)
	
	
	setframe = uicontrol('style','frame','pos',frpos);
	
	rad(1) = uicontrol('style','radio','pos',[(frleft+8) 13*txth 80 txth],...
		'string','Lines','value',rval1);

	rad(2) = uicontrol('style','radio','pos',[(frleft+pbwidth+18) 13*txth 80 txth],...
		'string','Arrows','value',rval2,'max',2);

	rad(3) = uicontrol('style','radio','pos',[frleft+2*pbwidth+28 13*txth 80 txth],...
		'string','None','value',rval3,'max',3);
				
	for i=1:3
		set(rad(i),'user',rad(:,[1:(i-1),(i+1):3]));
	end
	
	callrad = [
		'me = get(gcf,''currentobject'');',...
		'kk = get(me,''max'');',...
		'set(get(me,''user''),''value'',0),',...
		'set(me,''value'',kk),',...
		'data = get(gcf,''user'');',...
		'data(1) = kk;'...
		'set(gcf,''user'',data);'];
		
	set(rad,'call',callrad);

	call1 = [
		'me = get(gcf,''currentobject'');',...
		'kk = floor(str2num(get(me,''string'')));',...
		'[m,N] = computer;'...
		'if (N <= 8192),',...
		'	N = 32;',...
		'else,',...
		'	N = 50;',...
		'end,',...
		'kk = min([N,max([5,kk])]);'...
		'set(me,''string'',num2str(kk));'...
		'data = get(gcf,''user'');',...
		'data(2) = kk;',...
		'set(gcf,''user'',data);'];	
	
	settext(1) = uicontrol('style','text','pos',[3 11*txth txtl txth],...
		'horiz','left','string','Number of field points per row and column:  ');
		
	setedit(1) = uicontrol('style','edit','pos',[3+txtl 11*txth 100 txth],...
		'string',num2str(settings(2)),'call',call1);

	settext(2) = uicontrol('style','text','pos',[3 9*txth txtl txth],...
		'horiz','left','string','Relative size of calculation window:  ');
		
	kk = 1+2*settings(3);
	
	call2 =[
		'data = get(gcf,''user'');',...
		'ss = get(data(8),''string'');',...
		'data(3) = max(0,(str2num(ss)-1)/2);',...
		'set(data(8),''string'',ss);',...
		'set(gcf,''user'',data);'];
	
		
	setedit(2) = uicontrol('style','edit','pos',[3+txtl 9*txth 100 txth],...
		'string',num2str(kk),'call',call2);
		
	settext(3) = uicontrol('style','text','pos',[3 7*txth txtl txth],...
		'horiz','left','string','Minimum number of plot steps across the window:  ');

	call3 =[
		'data = get(gcf,''user'');',...
		'ss = max(round(str2num(get(data(9),''string''))),0);',...
		'data(4) = ss;',...
		'set(data(9),''string'',num2str(ss));',...
		'set(gcf,''user'',data);'];
		
	setedit(3) = uicontrol('style','edit','pos',[3+txtl 7*txth 100 txth],...
		'string',num2str(settings(4)),'call',call3);

	settext(4) = uicontrol('style','text','pos',[3 5*txth txtl txth],...
		'horiz','left','string','Maximum number of iterations per solution:  ');

	call4 =[
		'data = get(gcf,''user'');',...
		'data(5) = round(str2num(get(data(10),''string'')));',...
		'set(data(10),''string'',num2str(data(5)));',...
		'set(gcf,''user'',data);'];
		
	setedit(4) = uicontrol('style','edit','pos',[3+txtl 5*txth 100 txth],...
		'string',num2str(settings(5)),'call',call4);

	settext(5) = uicontrol('style','text','pos',[3 3*txth txtl txth],...
		'horiz','left','string','Relative error tolerance:  ');

	call5 =[
		'data = get(gcf,''user'');',...
		'data(6) = str2num(get(data(11),''string''));',...
		'set(data(11),''string'',num2str(data(6)));',...
		'set(gcf,''user'',data);'];
		
	setedit(5) = uicontrol('style','edit','pos',[3+txtl 3*txth 100 txth],...
		'string',num2str(settings(6)),'call',call5);

	bwidth = 130;
	spacing = (figwidth-2*bwidth-6)/3;
		
	setbutt(1) = uicontrol('style','push','pos',[3+spacing,txth,bwidth,txth],...
		'string','Cancel','call','close');
	
	setbutt(2) = uicontrol('style','push','pos',[3+2*spacing+bwidth,txth,bwidth,txth],...
		'string','Change settings','call','dfield(''setchange'')');
		
	set(dfsettings,'user',[settings,setedit]);

elseif strcmp(action,'setchange')

% 'setchange' is the callback for the Change button on the DFIELD Settings window.

	flag = 0;
	data = get(gcf,'user');
	settings = data(1:6);
	dfdisp = 0;
	figs = get(0,'children');
	for (figno = 1:length(figs));
		if (strcmp(get(figs(figno),'name'),'DFIELD Display')),
			dfdisp = figs(figno);
		end
	end
	if (dfdisp == 0)
		error('You must start DFIELD from the beginning.');
	else
		dh = get(dfdisp,'user');
		if settings(2)~=dh(20)
			flag = 1;
		elseif settings(1)~=dh(19)
			flag = 2;
		end
		dh(19:24) = settings;
		set(dfdisp,'user',dh);
	end
	dfset = 0;
	for (figno = 1:length(figs));
		if (strcmp(get(figs(figno),'name'),'DFIELD Setup'))
			dfset = figs(figno);
		end
	end
	if (dfset == 0)
		error('You must start DFIELD from the beginning.');
	else
		sh = get(dfset,'user');
		sh(29:34) = settings;
		set(dfset,'user',sh);
	end
	close
	if flag == 1
		dfield('dirfield');
	elseif flag == 2
		Arrflag = settings(1);
		arrh = get(dh(12),'user');
		ll = length(arrh)/2;
		if (Arrflag == 1)
			set(arrh(1:ll),'visible','on');
			set(arrh(ll+1:2*ll),'visible','off');
		elseif (Arrflag == 2)
			set(arrh(1:ll),'visible','off');
			set(arrh(ll+1:2*ll),'visible','on');
		else
			set(arrh(1:ll),'visible','of');
			set(arrh(ll+1:2*ll),'visible','off');
		end
		dfield('refresh');
	end
	

elseif strcmp(action,'delete')

% 'delete' is the callback for the Delete a graphics object selection
% on the menu.

	oldcall = get(gcf,'WindowButtonDownFcn');
	set(gcf,'WindowButtonDownFcn','');
	dh = get(gcf,'user');
	dm = get(dh(1),'user');
	arrh = get(dh(12),'user');
	v1 = get(arrh(1),'visible');
	v2 = get(arrh(2),'visible');
	set(arrh,'visible','off');
	dfield('refresh')	
	trjh = get(dh(3),'user');
	notice = dh(2:3);
	set(notice(1),'string','Select a graphics object with the mouse.');
	set(notice(2),'string','');
	ginput(1);
	objh = get(gcf,'currentobject');
	hc = [gcf gca dh(1:14)] - objh;
	if ( all(hc) ) 
		ah = find(trjh == objh);
		if (ah ~= [])
			trjh = [trjh(1:ah-1);trjh(ah+1:length(trjh))];
			set(dh(3),'user',trjh);
		end
		delete(objh); 
		set(notice(1),'string','Ready.');
		set(notice(2),'string',' ')
	else
		set(notice(1),'string','The selected object cannot be deleted.');
		set(notice(2),'string','Ready.')
	end
	set(arrh(1),'visible',v1);
	set(arrh(2),'visible',v2);
	set(gcf,'WindowButtonDownFcn',oldcall);

elseif strcmp(action,'refresh')

% 'refresh' is the callback for the Update the Display Window 
% selection from the menu.  It deletes the ends of orbits which 
% have been plotted using erasemode none, and it replots those 
% solutions so that they become children of the the display 
% window axes.

	dfdisp = 0;
	figs = get(0,'children');
	for (figno = 1:length(figs))
		if (strcmp(get(figs(figno),'name'),'DFIELD Display'))
			dfdisp = figs(figno);
		end
	end

	dh = get(dfdisp,'user');
	dm = get(dh(1),'user');
	dfdispa = dh(14);
	newtraj = get(dh(8),'user');
	trajh = get(dh(3),'user');
	axes(dfdispa);
	htemp = get(dfdispa,'user');
	if (htemp~=[])
		set(htemp,'erase','normal');
		delete(htemp);			% This deletes the orbit ends.
	end
	set(dfdispa,'user',[]);
	trjno = size(newtraj,2)/2;
	evens = [1:trjno]*2;
	odds = evens -1;
	newh = line(newtraj(:,odds),newtraj(:,evens),'linestyle','-','color','y');
	trajh = [trajh;newh(:)];
	drawnow
	set(dh(8),'user',[]);
	set(dh(3),'user',trajh);
	if (dh(7) > 4.0)
		set(dh(5),'enable','off');
	end
%	set(dh(5),'visible','off');

elseif strcmp(action,'text')

	dh = get(gcf,'user');
	notice = dh(2:3);
	set(notice(1),'string','Enter the text into the Command Window.');
	set(notice(2),'string',' ');

	oldcall = get(gcf,'WindowButtonDownFcn');
	set(gcf,'WindowButtonDownFcn','');

	txtstr = input('Enter the text here. >  ','s');
	set(notice(1),'string','Choose the location of the text.');
	gtext(txtstr);
	dfield('refresh');
	set(gcf,'WindowButtonDownFcn',oldcall);
	set(notice(1),'string','Ready.');

elseif strcmp(action,'print')

% 'print' is the callback of the Print button.  It first calls
% 'refresh', so that all orbit information is part of the axes, 
% and then it uses the standard MATLAB print command to print 
% the axes.

	dh = get(gcf,'user');
	dm = get(dh(1),'user');
	notice = dh(2:3);
	set(notice(1),'string','Preparing to print the DFIELD Display Window.');
	set(notice(2),'string','Please be patient.');
	dfdispa = dh(14);
	dfield('refresh')
	set(notice(1),'string','Printing the DFIELD Display Window.');
	print
	set(notice(1),'string','Ready.');
	set(notice(2),'string','');
	
	
elseif strcmp(action,'quit')

% 'quit' is the callback of the Quit buttons on teh DFIELD Setup and DFIELD
% Display windows.  It provides for an orderly exit, deleting all
% associated windows and the function m-file.

	figs = get(0,'children');
	dfdisp = 0;
	for (figno = 1:length(figs))
		nn = get(figs(figno),'name');
		if (length(nn) > 1)
			if (strcmp(nn,'DFIELD Display'))
				dfdisp = figs(figno);
				dh = get(dfdisp,'user');
				dm = get(dh(1),'user');
				FFFCCNNN = deblank(dm(3,:));
				if (exist(FFFCCNNN)==2) delete([FFFCCNNN,'.m']);end
				close(dfdisp)
			elseif (findstr(nn,'DFIELD')~=[])
				close(figs(figno))		
			end
		end
	end
end