fix property/global command

fix property/atom command

Syntax

fix id group property/atom variablename style restartvalue comm_ghost_value comm_reverse_ghost_value defaultvalue(s)...
fix id group property/global variablename style stylearg type type_value (warn_out_of_bounds val) defaultvalue(s)...
  • ID, group-ID are documented in fix command
  • property/global or property/atom = style name of this fix command
  • variablename = a valid C++ string

fix property/global:

  • style = scalar or vector or peratomtype or atomtype or matrix or atomtypepair or peratomtypepair
stylearg for scalar/vector: none
stylearg for matrix/atomtypepair: nCols
  • type = optional keyword, if available must be followed by:
  • type_value = constant or lookup
  • warn_out_of_bounds = optional keyword for type lookup
  • val = yes or no

fix property/atom:

  • style = scalar or vector
  • restartvalue = yes or no
  • communicate_ghost_value = yes or no
  • communicate_reverse_ghost_value = yes or no

Examples

fix m3 all property/global coefficientRestitution peratomtypepair 1 0.3
fix m5 all property/global characteristicVelocity scalar 2.
fix m5 all property/global initialTemperature peratomtype type lookup type1.csv type2.csv
fix uf all property/atom uf vector yes no no  0. 0. 0.

Description

Fix property/atom reserves per-atom properties to be accessed by the user or other fixes. Style scalar reserves one value per atom, style vector multiple values per atoms, where the number of defaultvalues (that are assigned to the atoms at creation) determines the length of the vector. The group of atoms the fix is applied to is always “all”, irrespective of which group is used for the fix command . If you want to assign different values for different groups, you can use the set command with keyword ‘property/atom’. Keyword restartvalues determines whether information about the values stored by this fix is written to binary restart files. Keyword communicate_ghost_value determines whether information about the values stored by this fix can be communicated to ghost particles (forward communication). The exact location during a time-step when this happens depends on the model that uses this fix. Keyword communicate_reverse_ghost_value determines whether information about the values stored by this fix can be communicated from ghost particles to owned particles (reverse communication). The exact location during a time-step when this happens depends on the model that uses this fix.

Fix property/global reserves global properties to be accessed by the user or other fixes or pair styles. The number of defaultvalues determines the length of the vector / the number of matrix components. For style vector, peratomtype or atomtype, the user provides the number of vector components. For style matrix, peratomtypepair or atomtypepair, the user provides the number of matrix columns (nCols).

Example: nCols*= 2 and *defaultvalues = 1 2 3 4 5 6 would be mapped into a matrix like

[ 1 2 ]

[ 3 4 ]

[ 5 6 ]

Note that the number of default values must thus be a multiple of nCols. Note that vector and **per***atomtype* do the same thing, **per***atomtype* is just provided to make input scripts more readable . Note that matrix and **per***atomtypepair* both refer to a matrix of global values. However, a matrix defined via **per***atomtypepair* is required to be symmetric.

The default values are floating point numbers by default. If the type keyword is used, then they are either floating point numbers or filenames if type_value is constant or lookup, respectively. The lookup type allows to specify a property that is a function of another variable. The function is specified pointwise in a file and a linear interpolation is performed between the points specified in the file. The file is structured as follows:

# Lines starting with '#' are ignored, e.g. for comments
0. 1.
1. 3.
2. 1.
6. 0.

Note that the entries in the first column must be listed in ascending order. This specific type can only be used in combination with specialized models. If the keyword warn_out_of_bounds is set to on, the fix issues a warning every time a function value is requested for an argument smaller than the first entry or larger than the last entry of the function file (in the above example: < 0 or > 6). This is useful if you are tuning parameters and don’t exactly know which range to expect.

Note that the group of atoms the fix is applied to is ignored (as the fix is not applied to atoms, but defines values of global scope).

Restart, fix_modify, output, run start/stop, minimize info

Information about this fix is written to binary restart files if you set restartvalue to ‘yes’.

Restrictions

none

Default

type_value = constant