|From:||Sonu Kumar <sonubwbs@...8...>|
|Date:||Thu, 24 Aug 2017 17:19:30 +0000|
Sorry for not providing exact description earlier.
I am trying to give an extra small perturbation in an already perturbed system that relates to calculation of lyapunov exponent.
Generally, the perturbations are given at t=0 in dynamical system but my idea revolved around adding an extra perturbation at each timestep to see how the system evolves. Now the calculation of lyapunov exponent can be done using an ideal trajectory and the perturbed trajectory. I already have the following :
I need the last :
3. Perturbed uniformly (Perturbation in displacement and velocity at every timestep with initial perturbation at t=0 being the same as 2)
I performed 1 normally.
I performed 2 as follows :
variable xpertub atom (random(-0.00000001, 0.00000001, 54851)
... (similary other variables)
displace_atoms active move v_xpertub v_ypertub 0 #active is the group on which I apply perturbations
velocity active set v_vpertub v_ypertub 0
and I proceed normally as done in 1
I couldn't perform 3 though. I though of applying pertubations in the form of fix addforce using variable style that generates random force which will be reflected as perturbations in velocity and displacement. However, the velocity and displacement perturbation shall be correlated due to addforce which I don't want.
I also thought of applying fix langevin but it will be basically be same thing as addforce with variable style. (I may be wrong here though).
From: Eric Murphy <murphyericjames@...24...>
Sent: Thursday, August 24, 2017 9:28 PM
To: Sonu Kumar
Cc: Steve Plimpton; email@example.com
Subject: Re: [lammps-users] Displacement Perturbations in lammps
Are you sure you aren't looking to simply add noise/a stochastic term to your equations of motion? Fix Langevin might be a good place to start.
On Wed, Aug 23, 2017 at 11:16 PM, Sonu Kumar <sonubwbs@...8...> wrote: