56 lines
1.3 KiB
ReStructuredText
56 lines
1.3 KiB
ReStructuredText
.. index:: compute momentum
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compute momentum command
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========================
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Syntax
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""""""
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.. code-block:: LAMMPS
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compute ID group-ID momentum
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* momentum = style name of this compute command
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Examples
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""""""""
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.. code-block:: LAMMPS
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compute 1 all momentum
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Description
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"""""""""""
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Define a computation that calculates the translational momentum *p*
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of a group of particles. It is computed as the sum
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:math:`\vec{p} = \sum_i m_i \cdot \vec{v}_i`
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over all particles in the compute group, where *m* and *v* are
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the mass and velocity vector of the particle, respectively.
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Output info
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"""""""""""
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This compute calculates a global vector (the summed momentum) of
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length 3. This value can be used by any command that uses a global
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vector value from a compute as input. See the :doc:`Howto output <Howto_output>` page for an overview of LAMMPS output
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options.
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The vector value calculated by this compute is "extensive". The vector
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value will be in mass\*velocity :doc:`units <units>`.
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Restrictions
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""""""""""""
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This compute is part of the EXTRA-COMPUTE package. It is only enabled if
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LAMMPS was built with that package. See the :doc:`Build package <Build_package>` page for more info.
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Related commands
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""""""""""""""""
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Default
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"""""""
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none
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