% num3plot.m 
% Generates three plots on page: Euler's method appxs on slope field; error of 
% Euler appx vs Runge-Kutta (4th order); Runge-Kutta (4th order) appxs on slope 
% field. 
% Requires the M-files INITN.M, EULSTDNT.M, SLOPEF.M RK4.M, HWSOL1.M. 
% INITN.M must be called first and contain appropriate entries for all 
% variables/parameters. 

figans=input('Do you already have a separate figure window for num3plot? (y/n) ','s'); 
if figans=='n'; 
 numfig=figure; 
end 
figure(numfig) 
clf 
set(numfig,'DefaultAxesFontSize',8) 

subplot(2,2,2) 
eulplot 
eulxmatr=xmatr; 

subplot(2,2,4) 
rk4plot	
rk4xmatr=xmatr; 

subplot(2,2,3) 
[u,v]=size(tmatr); 
cla 
hold on 
for j=1:length(hvec) 
	tplot=[]; xplot=[]; 
	for k=1:v 
		if tmatr(j,k)==0 & tmatr(j,k+1)==0 
			break 
		else 
			tplot=[tplot,tmatr(j,k)]; 
			xplot=[xplot,abs(eulxmatr(j,k)-rk4xmatr(j,k))];
		end 
	end 
	plot(tplot,xplot) 
end 
xlabel(['Error: Eul vs RK4, h=[',num2str(hvec),']']) 
hold off 
clear *xmatr