Young Modulus problem

Hi all... developers and users,

I am very new to LIGGGHTS and I have a question about an exercise:

# Using: LIGGGHTS (Version LIGGGHTS-PUBLIC 3.2.1)

# EXERCISE DESCRIPTION:
I have to insert a spherical particle (with no initial velocity) in a gravitational field, from an initial height of 10m. The particle can fall until a lower boundary (wall) set at 0 meters.
- In the "read.packing" you can see the 1) particle diameter 2) density 3) initial coordinates 4) velocities and 5) the box.
- The only force affecting the particle must be the gravitational force, therefore a vertical 1 D bounce is expected.

I am using Hertz, as contact model between wall and particle. I am conducting the same exercise in LIGGGHTS and MATLAB . in matlab I have conducted the same exercise in analytically and numerically, defining stiffness, viscosity and restitution as LIGGGHTS does (http://nf.nci.org.au/facilities/software/LIGGGHTS/doc/pair_gran.html)

# PROBLEM / QUESTION

If I solve the exercise analytically and numerically (in Matlab), the same bounce (plot of time - position) is obtained when the stiffness insert in both script of Matlab (both scripts) is equal to

Y = 5e6

While in the LIGGGHTS code is equal to

Y = 9.45e6

While Y should be the same every time, since in matlab I am basically copying how liggghts defines, variables in hertz, from Y* until the stiffness (see link)

Can anyone give me suggestions ??

## How to LIGGGHTS this exercise :

- After downloading and unzipping the folder "ballfallingandbouncing1D"
- Create an empty folder named "post"
- Run the "1_in_Ballfall" in LIGGGHTS
- Copy files from "2_ until 5_" into the post folder
- Run all files containing "matlab" in the name in matlab in order of number (from 2 until 5)

Greetings,
Luca