nice one Andres Fernando Pedraza, and Malory Johana Sanchez From Bogotá. Colombia!

just like to say the facebook fan page connected more people using Ejs to come here

this duffing oscillator is cool
and found another cool applets to understand the Ejs version one by  afpedraza
http://www.math.udel.edu/~hsiao/m302/JavaTools/osduffng.html
http://www.peter-junglas.de/fh/physbeans/applets/duffingoscillator.html
http://www.scholarpedia.org/article/Duffing_oscillator they look like this [img]http://www.scholarpedia.org/wiki/images/thumb/e/e5/Duffing-MagnetelasticBeam.gif/212px-Duffing-MagnetelasticBeam.gif[/img]
Duffing oscillator is an example of a periodically forced oscillator with a nonlinear elasticity, written as
[img]http://www.scholarpedia.org/wiki/images/math/d/e/c/dec8d87618e1acdcb45b70ea44786b31.png[/img](1),
where the damping constant obeys , and it is also known as a simple model which yields chaos, as well as van der Pol oscillator.

from http://dynlab.mpe.nus.edu.sg/mpelsb/me4213/Duffing.html
Duffing oscillator, a 2 degree of freedom oscillator with cubic stiffness.
x’’ + ax’ + x3 – x = b cos(t)
The oscillator can exhibit chaotic (i.e. irregular) oscillations

Question:
how come the applet is 2 mass oscillating so what is the difference between the red and blue mass?
i open the evolution page and study
dv/dt = -k1*x/m*s*(b*x*x-1)-R/m*v+A*Math.cos(w*t)
dv1/dt = -k1*x1/m*s*(b*x1*x1-1)-R/m*v1+A*Math.cos(w*t)

is it to show despite the same equation and same initial conditions, the red and blue mass ends up differently to show chaos?