# fix store/state command

## Syntax

    fix ID group-ID store/state N input1 input2 ... keyword value ...

-   ID, group-ID are documented in [fix](fix) command

-   store/state = style name of this fix command

-   N = store atom attributes every N steps, N = 0 for initial store
    only

-   input = one or more atom attributes

        possible attributes = id, mol, type, mass,
                              x, y, z, xs, ys, zs, xu, yu, zu, xsu, ysu, zsu, ix, iy, iz,
                              vx, vy, vz, fx, fy, fz,
                              q, mux, muy, muz, mu,
                              radius, diameter, omegax, omegay, omegaz,
                              angmomx, angmomy, angmomz, tqx, tqy, tqz,
                              c_ID, c_ID[I], f_ID, f_ID[I], v_name,
                              d_name, i_name, i2_name[I], d2_name[I],

        id = atom ID
        mol = molecule ID
        type = atom type
        mass = atom mass
        x,y,z = unscaled atom coordinates
        xs,ys,zs = scaled atom coordinates
        xu,yu,zu = unwrapped atom coordinates
        xsu,ysu,zsu = scaled unwrapped atom coordinates
        ix,iy,iz = box image that the atom is in
        vx,vy,vz = atom velocities
        fx,fy,fz = forces on atoms
        q = atom charge
        mux,muy,muz = orientation of dipolar atom
        mu = magnitued of dipole moment of atom
        radius,diameter = radius.diameter of spherical particle
        omegax,omegay,omegaz = angular velocity of spherical particle
        angmomx,angmomy,angmomz = angular momentum of aspherical particle
        tqx,tqy,tqz = torque on finite-size particles
        *c_ID* = per-atom vector calculated by a compute with ID
        *c_ID[I]* = Ith column of per-atom array calculated by a compute with ID
        *f_ID* = per-atom vector calculated by a fix with ID
        *f_ID[I]* = Ith column of per-atom array calculated by a fix with ID
        *v_name* = per-atom vector calculated by an atom-style variable with name
        *i_name* = custom integer vector with name
        *d_name* = custom floating point vector with name
        *i2_name[I]* = Ith column of custom integer array with name
        *d2_name[I]* = Ith column of custom floating-point array with name

-   zero or more keyword/value pairs may be appended

-   keyword = *com*

        *com* value = *yes* or *no*

## Examples

``` LAMMPS
fix 1 all store/state 0 x y z
fix 1 all store/state 0 xu yu zu com yes
fix 2 all store/state 1000 vx vy vz
```

## Description

Define a fix that stores attributes for each atom in the group at the
time the fix is defined. If *N* is 0, then the values are never updated,
so this is a way of archiving an atom attribute at a given time for
future use in a calculation or output. See the discussion of [output
commands](Howto_output) that take fixes as inputs.

If *N* is not zero, then the attributes will be updated every *N* steps.

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

Actually, only atom attributes specified by keywords like *xu* or *vy*
or *radius* are initially stored immediately at the point in your input
script when the fix is defined. Attributes specified by a compute, fix,
or variable are not initially stored until the first run following the
fix definition begins. This is because calculating those attributes may
require quantities that are not defined in between runs.
::::

The list of possible attributes is the same as that used by the [dump
custom](dump) command, which describes their meaning.

If the *com* keyword is set to *yes* then the *xu*, *yu*, and *zu*
inputs store the position of each atom relative to the center-of-mass of
the group of atoms, instead of storing the absolute position.

The requested values are stored in a per-atom vector or array as
discussed below. Zeroes are stored for atoms not in the specified group.

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

This fix writes the per-atom values it stores to [binary restart
files](restart), so that the values can be restored when a simulation is
restarted. See the [read_restart](read_restart) command for info on how
to re-specify a fix in an input script that reads a restart file, so
that the operation of the fix continues in an uninterrupted fashion.

:::: warning
::: title
Warning
:::

When reading data from a restart file, this fix command has to be
specified **exactly** the same way as before. LAMMPS will only check
whether a fix is of the same style and has the same fix ID and in case
of a match will then try to initialize the fix with the data stored in
the binary restart file. If the fix store/state command does not match
exactly, data can be corrupted or LAMMPS may crash.
::::

None of the [fix_modify](fix_modify) options are relevant to this fix.

If a single input is specified, this fix produces a per-atom vector. If
multiple inputs are specified, a per-atom array is produced where the
number of columns for each atom is the number of inputs. These can be
accessed by various [output commands](Howto_output). The per-atom values
be accessed on any timestep.

No parameter of this fix can be used with the *start/stop* keywords of
the [run](run) command. This fix is not invoked during [energy
minimization](minimize).

## Restrictions

> none

## Related commands

[dump custom](dump), [compute property/atom](compute_property_atom),
[fix property/atom](fix_property_atom), [variable](variable)

## Default

The option default is com = no.