# compute smd/tlsph/defgrad command

## Syntax

    compute ID group-ID smd/tlsph/defgrad

-   ID, group-ID are documented in [compute](compute) command
-   smd/tlsph/defgrad = style name of this compute command

## Examples

``` LAMMPS
compute 1 all smd/tlsph/defgrad
```

## Description

Define a computation that calculates the deformation gradient. It is
only meaningful for particles which interact according to the
Total-Lagrangian SPH pair style.

See [this PDF guide](PDF/MACHDYN_LAMMPS_userguide.pdf)\_ to use Smooth
Mach Dynamics in LAMMPS.

## Output info

This compute outputs a per-particle vector of vectors (tensors), which
can be accessed by any command that uses per-particle values from a
compute as input. See the [Howto output](Howto_output) doc page for an
overview of LAMMPS output options.

The per-particle vector values will be given dimensionless. See
[units](units). The per-particle vector has 10 entries. The first nine
entries correspond to the xx, xy, xz, yx, yy, yz, zx, zy, zz components
of the asymmetric deformation gradient tensor. The tenth entry is the
determinant of the deformation gradient.

## Restrictions

This compute is part of the MACHDYN package. It is only enabled if
LAMMPS was built with that package. See the [Build
package](Build_package) page for more info. TThis compute can only be
used for particles which interact via the total Lagrangian SPH pair
style.

## Related commands

[smd/hourglass/error](compute_smd_hourglass_error)

## Default

none