// Diagrama de fase

deff('[xprima] = ej1(t,x)','xprima = [-1 0;0 -4]*x') 
clf
t = 0:0.1:100
xf = linspace(-4,4,10);yf = linspace(-4,4,6)
for i = 1:length(xf)
    for j = 1:length(yf)
        x = ode([xf(i);yf(j)],0,t,ej1)
    plot(x(1,:),x(2,:))
    end
end
fchamp(ej1,0,xf,yf)
xlabel('x1');ylabel('x2')
