# compute count/type command

## Syntax

``` LAMMPS
compute ID group-ID count/type mode
```

-   ID, group-ID are documented in [compute](compute) command
-   count/type = style name of this compute command
-   mode = {atom} or {bond} or {angle} or {dihedral} or {improper}

## Examples

``` LAMMPS
compute 1 all count/type atom
compute 1 flowmols count/type bond
```

## Description

::: versionadded
15Jun2023
:::

Define a computation that counts the current number of atoms for each
atom type. Or the number of bonds (angles, dihedrals, impropers) for
each bond (angle, dihedral, improper) type.

The former can be useful if atoms are added to or deleted from the
system in random ways, e.g. via the [fix deposit](fix_deposit), [fix
pour](fix_pour), or [fix evaporate](fix_evaporate) commands. The latter
can be useful in reactive simulations where molecular bonds are broken
or created, as well as angles, dihedrals, impropers.

Note that for this command, bonds (angles, etc) are the topological kind
enumerated in a data file, initially read by the [read_data](read_data)
command or defined by the [molecule](molecule) command. They do not
refer to implicit bonds defined on-the-fly by bond-order or reactive
pair styles based on the current conformation of small clusters of
atoms.

These commands can turn off topological bonds (angles, etc) by setting
their bond (angle, etc) types to negative values. This command includes
the turned-off bonds (angles, etc) in the count for each type:

-   [fix shake](fix_shake)
-   [delete_bonds](delete_bonds)

These commands can create and/or break topological bonds (angles, etc).
In the case of breaking, they remove the bond (angle, etc) from the
system, so that they no longer exist ([bond_style quartic](bond_quartic)
and [BPM bond styles](Howto_bpm) are exceptions, see the discussion
below). Thus they are not included in the counts for each type:

-   [delete_bonds remove](delete_bonds)
-   [bond_style quartic](bond_quartic)
-   [fix bond/react](fix_bond_react)
-   [fix bond/create](fix_bond_create)
-   [fix bond/break](fix_bond_break)
-   [BPM package](Howto_bpm) bond styles

------------------------------------------------------------------------

If the {mode} setting is {atom} then the count of atoms for each atom
type is tallied. Only atoms in the specified group are counted.

If the {mode} setting is {bond} then the count of bonds for each bond
type is tallied. Only bonds with both atoms in the specified group are
counted.

For {mode} = {bond}, broken bonds with a bond type of zero are also
counted. The [bond_style quartic](bond_quartic) and [BPM bond
styles](Howto_bpm) break bonds by doing this. See the [Howto broken
bonds](Howto_broken_bonds) doc page for more details. Note that the
group setting is ignored for broken bonds; all broken bonds in the
system are counted.

If the {mode} setting is {angle} then the count of angles for each angle
type is tallied. Only angles with all 3 atoms in the specified group are
counted.

If the {mode} setting is {dihedral} then the count of dihedrals for each
dihedral type is tallied. Only dihedrals with all 4 atoms in the
specified group are counted.

If the {mode} setting is {improper} then the count of impropers for each
improper type is tallied. Only impropers with all 4 atoms in the
specified group are counted.

------------------------------------------------------------------------

## Output info

This compute calculates a global vector of counts. If the mode is {atom}
or {bond} or {angle} or {dihedral} or {improper}, then the vector length
is the number of atom types or bond types or angle types or dihedral
types or improper types, respectively.

If the mode is {bond} this compute also calculates a global scalar which
is the number of broken bonds with type = 0, as explained above.

These values can be used by any command that uses global scalar or
vector values from a compute as input. See the [Howto
output](Howto_output) page for an overview of LAMMPS output options.

The scalar and vector values calculated by this compute are
\"extensive\".

## Restrictions

none

## Related commands

none

## Default

none