115 lines
3.9 KiB
ReStructuredText
115 lines
3.9 KiB
ReStructuredText
.. index:: compute property/grid
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compute property/grid command
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=============================
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Syntax
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""""""
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.. parsed-literal::
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compute ID group-ID property/grid Nx Ny Nz input1 input2 ...
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* property/grid = style name of this compute command
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* Nx, Ny, Nz = grid size in each dimension
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* input1,etc = one or more attributes
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.. parsed-literal::
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attributes = id, ix, iy, iz, x, y, z, xs, ys, zs, xc, yc, zc, xsc, ysc, zsc
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id = ID of grid cell, x fastest, y next, z slowest
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ix,iy,iz = grid indices in each dimension (1 to N inclusive)
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x,y,z = coords of lower left corner of grid cell
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xs,ys,zs = scaled coords of lower left corner of grid cell (0.0 to 1.0)
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xc,yc,zc = coords of center point of grid cell
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xsc,ysc,zsc = scaled coords of center point of grid cell (0.0 to 1.0)
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Examples
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""""""""
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.. code-block:: LAMMPS
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compute 1 all property/grid id ix iy iz
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compute 1 all property/grid id xc yc zc
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Description
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"""""""""""
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Define a computation that stores the specified attributes of a
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distributed grid. In LAMMPS, distributed grids are regular 2d or 3d
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grids which overlay a 2d or 3d simulation domain. Each processor owns
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the grid cells whose center points lie within its sub-domain. See the
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:doc:`Howto grid <Howto_grid>` doc page for details of how distributed
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grids can be defined by various commands and referenced.
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This compute stores the specified attributes of grids as per-grid data
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so they can be accessed by other :doc:`output commands <Howto_output>`
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such as :doc:`dump grid <dump>`.
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*Nx*, *Ny*, and *Nz* define the size of the grid. For a 2d simulation
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*Nz* must be 1. When this compute is used by :doc:`dump grid <dump>`,
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to output per-grid values from other computes of fixes, the grid size
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specified for this command must be consistent with the grid sizes
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used by the other commands.
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The *id* attribute stores the grid ID for each grid cell. For a
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global grid of size Nx by Ny by Nz (in 3d simulations) the grid IDs
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range from 1 to Nx*Ny*Nz. They are ordered with the X index of the 3d
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grid varying fastest, then Y, then Z slowest. For 2d grids (in 2d
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simulations), the grid IDs range from 1 to Nx*Ny, with X varying
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fastest and Y slowest.
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The *ix*, *iy*, *iz* attributes are the indices of a grid cell in
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each dimension. They range from 1 to Nx inclusive in the X dimension,
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and similar for Y and Z.
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The *x*, *y*, *z* attributes are the coordinates of the lower left
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corner point of each grid cell.
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The *xs*, *ys*, *zs* attributes are also coordinates of the lower left
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corner point of each grid cell, except in scaled coordinates, where
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the lower-left corner of the entire simulation box is (0,0,0) and the
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upper right corner is (1,1,1).
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The *xc*, *yc*, *zc* attributes are the coordinates of the center
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point of each grid cell.
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The *xsc*, *ysc*, *zsc* attributes are also coordinates of the center
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point each grid cell, except in scaled coordinates, where the
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lower-left corner of the entire simulation box is (0,0,0) and the upper
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right corner is (1,1,1).
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For :doc:`triclinic simulation boxes <Howto_triclinic>`, the grid
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point coordinates for (x,y,z) and (xc,yc,zc) will reflect the
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triclinic geometry. For (xs,yz,zs) and (xsc,ysc,zsc), the coordinates
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are the same for orthogonal versus triclinic boxes.
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Output info
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"""""""""""
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This compute calculates a per-grid vector or array depending on the
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number of input values. The length of the vector or number of array
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rows (distributed across all processors) is Nx * Ny * Nz. For access
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by other commands, the name of the single grid produced by this
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command is "grid". The name of its per-grid data is "data".
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The (x,y,z) and (xc,yc,zc) coordinates are in distance :doc:`units
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<units>`.
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Restrictions
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""""""""""""
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For 2d simulations, the attributes which refer to
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the Z dimension cannot be used.
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Related commands
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""""""""""""""""
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:doc:`dump grid <dump>`
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Default
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"""""""
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none
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