# compute com command

## Syntax

``` LAMMPS
compute ID group-ID com
```

-   ID, group-ID are documented in [compute](compute) command
-   com = style name of this compute command

## Examples

``` LAMMPS
compute 1 all com
```

## Description

Define a computation that calculates the center-of-mass of the group of
atoms, including all effects due to atoms passing through periodic
boundaries.

A vector of three quantities is calculated by this compute, which are
the $(x,y,z)$ coordinates of the center of mass.

:::: note
::: title
Note
:::

The coordinates of an atom contribute to the center-of-mass in
\"unwrapped\" form, by using the image flags associated with each atom.
See the [dump custom](dump) command for a discussion of \"unwrapped\"
coordinates. See the Atoms section of the [read_data](read_data) command
for a discussion of image flags and how they are set for each atom. You
can reset the image flags (e.g., to 0) before invoking this compute by
using the [set image](set) command.
::::

## Output info

This compute calculates a global vector of length 3, which can be
accessed by indices 1\--3 by any command that uses global vector values
from a compute as input. See the [Howto output](Howto_output) doc page
for an overview of LAMMPS output options.

The vector values are \"intensive\". The vector values will be in
distance [units](units).

## Restrictions

> none

## Related commands

[compute com/chunk](compute_com_chunk)

## Default

none