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# LIGGGHTS 3.X vs. LIGGGHTS 2.X - syntax changes

## Introduction:

This is a short outline of the most important changes in LIGGGHTS 3.X compared to LIGGGHTS 2.X regarding the syntax of major commands. The motivation for these changes was to make the script language more readable and to improve extendability (in the sense of object oriented programming) with respect to modelling approaches.

## Commands covered by this tutorial:

- fix wall/gran/*
- pair_style gran/*

  ## Changes in syntax for each command:

  Changes are indicated as follows

      OLD: old_syntax
      NEW: new_syntax

  where old_syntax refers to the syntax used in LIGGGHTS 2.X and before, and new_syntax refers to the syntax used in LIGGGHTS 3.X.

  fix wall/gran/*:

      OLD: fix ID group-ID wall/gran/* WALL-OPTIONS
      NEW: fix ID group-ID wall/gran MODEL-SELECTION WALL-OPTIONS MODEL-SETTINGS

  ### MODEL-SELECTION

      MODEL-SELECTION = model M [tangential T] [cohesion C] [rolling_friction R]

      M = hooke | hooke_stiffness | hooke_hysteresis | hertz | hertz_stiffness

      T = no_history | history

      C = off | sjkr | sjkr2 | hamaker

      R = off | cdt | epsd

  ### MODEL-SETTINGS

      MODEL-SELECTION = [tangential_damping (on|off)] [absolute_damping (on|off)] [viscous (on|off)]

  ### Examples

      OLD: fix ID group-ID wall/gran/hertz/history mesh n_meshes 2 meshes cad1 cad2
      NEW: fix ID group-ID wall/gran model hertz tangential history mesh n_meshes 2 meshes cad1 cad2

      OLD: fix ID1 group-ID wall/gran/hooke/history type 1 xplane -0.5
      NEW: fix ID1 group-ID wall/gran model hooke tangential history type 1 xplane -0.5

      OLD: fix ID1 group-ID wall/gran/hertz/history primitive type 1 xplane -0.5 rolling_friction cdt
      NEW: fix ID1 group-ID wall/gran model hertz tangential history rolling_friction cdt primitive type 1 xplane -0.5

      OLD: fix ID group-ID wall/gran/hertz/history primitive type 1 xplane -0.5 0.5 cohesion sjkr
      NEW: fix ID group-ID wall/gran model hertz tangential history cohesion sjkr primitive type 1 xplane -0.5 0.5

      OLD: fix ID group-ID wall/gran/hertz/history primitive type 1 zcylinder 0.05 0. 0. tangential_damping off
      NEW: fix ID group-ID wall/gran model hertz tangential history primitive type 1 zcylinder 0.05 0. 0. tangential_damping off

  pair_style gran/*:

      OLD: pair_style gran/* MODEL-SETTINGS
      NEW: pair_style gran  MODEL-SELECTION MODEL-SETTINGS

  ### MODEL-SELECTION

  Same as in fix wall/gran/*

  ### MODEL-SETTINGS

  Same as in fix wall/gran/*

  ### Examples

      OLD: pair_style gran/hertz/history
      NEW: pair_style gran model hertz tangential history

      OLD: pair_style gran/hertz/history rolling_friction cdt
      NEW: pair_style gran model hertz tangential history rolling_friction cdt

      OLD: pair_style gran/hertz/history cohesion sjkr
      NEW: pair_style gran model hertz tangential history cohesion sjkr

      OLD: pair_style gran/hertz/history tangential_damping off
      OLD: pair_style gran model hertz tangential history tangential_damping off