# compute_modify command

## Syntax

``` LAMMPS
compute_modify compute-ID keyword value ...
```

-   compute-ID = ID of the compute to modify

-   one or more keyword/value pairs may be listed

-   keyword = *extra/dof* or *extra* or *dynamic/dof* or *dynamic*

        *extra/dof* value = N
          N = # of extra degrees of freedom to subtract
        *extra* syntax is identical to *extra/dof*, will be disabled at some point
        *dynamic/dof* value = *yes* or *no*
          yes/no = do or do not re-compute the number of degrees of freedom (DOF) contributing to the temperature
        *dynamic* syntax is identical to *dynamic/dof*, will be disabled at some point

## Examples

``` LAMMPS
compute_modify myTemp extra/dof 0
compute_modify newtemp dynamic/dof yes extra/dof 600
```

## Description

Modify one or more parameters of a previously defined compute. Not all
compute styles support all parameters.

The *extra/dof* or *extra* keyword refers to how many degrees of freedom
are subtracted (typically from $3N$) as a normalizing factor in a
temperature computation. Only computes that compute a temperature use
this option. The default is 2 or 3 for [2d or 3d systems](dimension)
which is a correction factor for an ensemble of velocities with zero
total linear momentum. For compute temp/partial, if one or more velocity
components are excluded, the value used for *extra* is scaled
accordingly. You can use a negative number for the *extra* parameter if
you need to add degrees-of-freedom. See the [compute
temp/asphere](compute_temp_asphere) command for an example.

The *dynamic/dof* or *dynamic* keyword determines whether the number of
atoms $N$ in the compute group and their associated degrees of freedom
(DOF) are re-computed each time a temperature is computed. Only compute
styles that calculate a temperature use this option. By default, $N$ and
their DOF are assumed to be constant. If you are adding atoms or
molecules to the system (see the [fix pour](fix_pour), [fix
deposit](fix_deposit), and [fix gcmc](fix_gcmc) commands) or expect
atoms or molecules to be lost (e.g. due to exiting the simulation box or
via [fix evaporate](fix_evaporate)), then this option should be used to
ensure the temperature is correctly normalized.

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

The *extra* and *dynamic* keywords should not be used as they are
deprecated (March 2017) and will eventually be disabled. Instead, use
the equivalent *extra/dof* and *dynamic/dof* keywords.
::::

## Restrictions

> none

## Related commands

[compute](compute)

## Default

The option defaults are extra/dof = 2 or 3 for 2d or 3d systems and
dynamic/dof = *no*.