## group_num

### Syntax

group_num new_group_number restart_group_number fix_number cal_number

• new_group_number, restart_group_number, fix_number, cal_number = non-negative integer (<= 40)

### Examples

group_num 3 0 3 0
group_num 2 1 1 2


### Description

This command sets the numbers of new groups, restart groups, fix, and calculations. In CAC, a group is a collection of elements/nodes/atoms. There are two purposes of having groups: (i) to apply a displacement/force to certain elements/nodes/atoms, (ii) to calculate some mechanical quantities, e.g., energy, force, and stress, of certain elements/nodes/atoms.

The new groups are defined in the group command. The elements/nodes/atoms contained in the restart groups, named group_*, are read from the group_in_*.id files, where * is a positive integer starting from new_group_number + 1, yet their displacement/force information is set in the fix command.

The total number of groups, i.e., new_group_number + restart_group_number, cannot be larger than 40. Files group_in_*.id contain information of the restart groups. On the one hand, there cannot be fewer group_in_*.id files than restart_group_number; on the other hand, any group_in_*.id file with * > new_group_number + restart_group_number will be ignored. When boolean_restart = f, restart_group_number becomes 0, regardless of its value set in this command.

fix_number should not be larger than new_group_number + restart_group_number; neither should cal_number. Also, fix_number + cal_number should not be smaller than new_group_number + restart_group_number.

The new groups are defined in the group command. The displacement/force and calculation information of each group is set in the fix and cal commands, respectively.

group.f90, fix_displacement.f90, fix_force.f90, group_cal.f90

### Default

group_num 0 0 0 0