function system
    [x,y]=dsolve('Dx=-2*x-4*y','Dy=2*x+2*y','x(0)=1','y(0)=-1')
    s=-5:0.01:5;
    X=subs(x,'t',s);
    Y=subs(y,'t',s);
    plot(s,X,s,Y)
    %plot(X,Y)

end

