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# compute smd/hourglass/error command

## Syntax

    compute ID group-ID smd/hourglass/error

- ID, group-ID are documented in compute command

- smd/hourglass/error = style name of this compute command

## Examples

    compute 1 all smd/hourglass/error

## Description

Define a computation which outputs the error of the approximated relative separation with respect to the actual relative separation of the particles i and j. Ideally, if the deformation gradient is exact, and there exists a unique mapping between all particles’ positions within the neighborhood of the central node and the deformation gradient, the approximated relative separation will coincide with the actual relative separation of the particles i and j in the deformed configuration. This compute is only really useful for debugging the hourglass control mechanism which is part of 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, 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 values will are dimensionless. See units.

## 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 tlsph pair style.

## Related commands

smd/tlsph_defgrad

## Default