1.1.4. Per-atom properties — LAMMPS documentation

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# 1.1.4. Per-atom properties

This section documents the following functions:

- `lammps_extract_atom_datatype()`

- `lammps_extract_atom()`

int lammps_extract_atom_datatype(void *handle, const char *name)

  Get data type of a LAMMPS per-atom property

  New in version 18Sep2020.

  This function returns an integer that encodes the data type of the per-atom property with the specified name. See `_LMP_DATATYPE_CONST` for valid values. Callers of `lammps_extract_atom()` can use this information to then decide how to cast the `void *` pointer and access the data.

  Parameters:

    - handle – pointer to a previously created LAMMPS instance

    - name – string with the name of the extracted property

  Returns:

    integer constant encoding the data type of the property or -1 if not found.

void *lammps_extract_atom(void *handle, const char *name)

  Get pointer to a LAMMPS per-atom property.

  This function returns a pointer to the location of per-atom properties (and per-atom-type properties in the case of the ‘mass’ keyword). Per-atom data is distributed across sub-domains and thus MPI ranks. The returned pointer is cast to `void *` and needs to be cast to a pointer of data type that the entity represents.

  A table with supported keywords is included in the documentation of the `Atom::extract()` function.

  Warning

  The pointers returned by this function are generally not persistent since per-atom data may be re-distributed, re-allocated, and re-ordered at every re-neighboring operation.

  Parameters:

    - handle – pointer to a previously created LAMMPS instance

    - name – string with the name of the extracted property

  Returns:

    pointer (cast to `void *`) to the location of the requested data or `NULL` if not found.