NXcg_grid

Status:

base class, extends NXobject

Description:

Computational geometry description of a Wigner-Seitz cell grid in Euclidean space.

Frequently convenient three-dimensional grids with cubic cells are used. Exemplar applications are spectral-solver based crystal plasticity and stencil methods like phase-field or cellular automata.

Symbols:

The symbols used in the schema to specify e.g. dimensions of arrays.

d: The dimensionality of the grid.

c: The cardinality or total number of cells/grid points.

n_b: Number of boundaries of the bounding box or primitive to the grid.

Groups cited:

NXcg_polyhedron_set, NXtransformations

Structure:

dimensionality: (optional) NX_POSINT {units=NX_UNITLESS}

Any of these values: 1 | 2 | 3

cardinality: (optional) NX_POSINT {units=NX_UNITLESS}

origin: (optional) NX_NUMBER (Rank: 1, Dimensions: [d])

symmetry: (optional) NX_CHAR

The symmetry of the lattice defining the shape of the unit cell.

Obligatory value: cubic

cell_dimensions: (optional) NX_NUMBER (Rank: 1, Dimensions: [d]) {units=NX_LENGTH}

The unit cell dimensions using crystallographic notation.

extent: (optional) NX_POSINT (Rank: 1, Dimensions: [d]) {units=NX_UNITLESS}

Number of unit cells along each of the d unit vectors. The total number of cells, or grid points has to be the cardinality. If the grid has an irregular number of grid positions in each direction, as it could be for instance the case of a grid where all grid points outside some masking primitive are removed, this extent field should not be used. Instead use the coordinate field.

identifier_offset: (optional) NX_INT {units=NX_UNITLESS}

Integer which specifies the first index to be used for distinguishing identifiers for cells. Identifiers are defined either implicitly or explicitly. For implicit indexing the identifiers are defined on the interval [identifier_offset, identifier_offset+c-1]. For explicit indexing the identifier array has to be defined.

The identifier_offset field can for example be used to communicate if the identifiers are expected to start from 1 (referred to as Fortran-/Matlab-) or from 0 (referred to as C-, Python-style index notation) respectively.

identifier: (optional) NX_INT (Rank: 1, Dimensions: [c]) {units=NX_UNITLESS}

Integer used to distinguish cells for explicit indexing.

position: (optional) NX_NUMBER (Rank: 2, Dimensions: [c, d]) {units=NX_LENGTH}

Position of each cell in Euclidean space.

coordinate: (optional) NX_INT (Rank: 2, Dimensions: [c, d]) {units=NX_DIMENSIONLESS}

Coordinate of each cell with respect to the discrete grid.

number_of_boundaries: (optional) NX_POSINT {units=NX_UNITLESS}

How many distinct boundaries are distinguished? Most grids discretize a cubic or cuboidal region. In this case six sides can be distinguished, each making an own boundary.

boundaries: (optional) NX_CHAR

Name of the boundaries. E.g. left, right, front, back, bottom, top, The field must have as many entries as there are number_of_boundaries.

boundary_conditions: (optional) NX_INT (Rank: 1, Dimensions: [n_b]) {units=NX_UNITLESS}

The boundary conditions for each boundary:

0 - undefined 1 - open 2 - periodic 3 - mirror 4 - von Neumann 5 - Dirichlet

TRANSFORMATIONS: (optional) NXtransformations

Reference to or definition of a coordinate system with which the positions and directions are interpretable.

bounding_box: (optional) NXcg_polyhedron_set

A tight bounding box or sphere or bounding primitive about the grid.

Hypertext Anchors

List of hypertext anchors for all groups, fields, attributes, and links defined in this class.

NXDL Source:

https://github.com/FAIRmat-Experimental/nexus_definitions/tree/fairmat/contributed_definitions/NXcg_grid.nxdl.xml