function kefrendszer(f1,f2,x0,y10,y20,xmax,kmax)
close all
x=linspace(x0,xmax,kmax+1);
y1=zeros(1,kmax+1); y2=y1;
h=(xmax-x0)/kmax;
y1(1)=y10; y2(1)=y20; 
for k=1:kmax
   y1(k+1)=y1(k)+h*f1(x(k),y1(k),y2(k));
   y2(k+1)=y2(k)+h*f2(x(k),y1(k),y2(k));
end;
plot(x,y1,'bo-',x,y2,'go-')
legend('y1','y2')
pause
plot(y1,y2,'bo-')
xlabel('y1'), ylabel('y2')  
title('Fáziskép')
