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# compute smd/tlsph/shape command

## Syntax

    compute ID group-ID smd/tlsph/shape

- ID, group-ID are documented in compute command

- smd/tlsph/shape = style name of this compute command

## Examples

    compute 1 all smd/tlsph/shape

## Description

Define a computation that outputs the current shape of the volume associated with a particle as a rotated ellipsoid. It is only meaningful for particles which interact according to the Total-Lagrangian SPH pair style.

See this PDF guide to use Smooth Mach Dynamics in LAMMPS.

## Output info

This compute calculates a per-particle vector of vectors, which can be accessed by any command that uses per-particle values from a compute as input. See the Howto output page for an overview of LAMMPS output options.

The per-particle vector has 7 entries. The first three entries correspond to the lengths of the ellipsoid’s axes and have units of length. These axis values are computed as the contact radius times the xx, yy, or zz components of the Green-Lagrange strain tensor associated with the particle. The next 4 values are quaternions (order: q, x, y, z) which describe the spatial rotation of the particle relative to its initial state.

## Restrictions

This compute is part of the MACHDYN package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.

This quantity will be computed only for particles which interact with the Total-Lagrangian SPH pair style.

## Related commands

smd/contact/radius

## Default

none