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# Variables
Variables frequently used in C-API are explained. In interfaces of
other languages, the definition may be different, e.g., `lattice`
for Python interface is transposed.
(variables_lattice)=
## `lattice`
**Attention**: In Python interface, `lattice` is transposed
[](#py_variables_crystal_structure).
Basis vectors (in Cartesian coordinates)
```
[ [ a_x, b_x, c_x ],
[ a_y, b_y, c_y ],
[ a_z, b_z, c_z ] ]
```
See [Basis vectors](#def_basis_vectors) and [Atomic point
coordinates](#def_point_coordinates) for more details.
## `position`
Atomic points (in fractional coordinates with respect to basis vectors)
```
[ [ x1_1, x1_2, x1_3 ],
[ x2_1, x2_2, x2_3 ],
[ x3_1, x3_2, x3_3 ],
... ]
```
See [Basis vectors](#def_basis_vectors) and [Atomic point
coordinates](#def_point_coordinates) for more details.
## `types`
Atomic species are differentiated by integers. The numbers are just
used to distinguishes atoms, and is not related to atomic numbers.
```
[ type_1, type_2, type_3, ... ]
```
The number of elements is same as the number of atoms.
## `rotation`
Rotation matrices (integer) of symmetry operations.
```
[ [ W_11, W_12, W_13 ],
[ W_21, W_22, W_23 ],
[ W_31, W_32, W_33 ] ]
```
See [Symmetry operation](#def_symmetry_operation) for more details.
## `translation`
Translation vectors corresponding to symmetry operations in fractional
coordinates.
```
[ w_1, w_2, w_3 ]
```
See [Symmetry operation](#def_symmetry_operation) for more details.
(variables_symprec)=
## `symprec`
Distance tolerance in Cartesian coordinates to find crystal
symmetry.
For atomic positions, roughly speaking, two position vectors `x` and `x'` in
Cartesian coordinates are considered to be the same if `|x' - x| < symprec`.
For more details, see the [spglib paper](https://arxiv.org/abs/1808.01590),
Sec. II-A.
The angle distortion between basis vectors is converted to a length
and compared with this distance tolerance. For more details, see the
[spglib paper](https://arxiv.org/abs/1808.01590), Sec. IV-A. It is
possible to specify angle tolerance explicitly, see
[](#variables_angle_tolerance).
(variables_angle_tolerance)=
## `angle_tolerance`
Tolerance of angle between basis vectors in degrees to be tolerated
in the symmetry finding. To use angle tolerance, another set of
functions are prepared for C-API as follows
```
spgat_get_dataset
spgat_get_symmetry
spgat_get_symmetry_with_collinear_spin
spgat_get_multiplicity
spgat_find_primitive
spgat_get_international
spgat_get_schoenflies
spgat_refine_cell
```
(variables_mag_symprec)=
## `mag_symprec`
Tolerance for magnetic symmetry search in the unit of spins or magmoms. By
specifying a negative value, the same value as `symprec` is used to compare
magnetic moments.
The following functions are called by the same way with an additional argument
of `const double angle_tolerance` in degrees. By specifying a negative value,
the behavior becomes the same as usual functions (e.g.
`spg_get_magnetic_dataset`). For python-API, the magnetic tolerance is given
with a keyword argument of `mag_symprec`, where the default value of
`mag_symprec` is a negative value.
```
spgms_get_magnetic_dataset
spgms_get_symmetry_with_collinear_spin
spgms_get_symmetry_with_site_tensors
```
|
