> with(plots):

Warning, the name changecoords has been redefined

> with(DEtools):

> DEplot([diff(x(t),t)=y(t),diff(y(t),t)=-0.5*y(t)-9*x(t)-2*x(t)^3],[x(t),y(t)],0..1.5,{[0,0,1],[0,1,0],[0,0,-1],[0,-1,0],[0,0,10],[0,5,0]},color=y^2+9*x^2+(1/2)*x^4,arrows=THICK,stepsize=.006, title=`damped hard oscillator, color=energy`,linecolor=black);