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add notes to python versions of lammps_extract_fix() that for global data one can only retrieve scalars

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Axel Kohlmeyer
2024-03-19 22:39:05 -04:00
parent d0e2a846b2
commit 2dd9560439
3 changed files with 26 additions and 10 deletions
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26
python/lammps/core.py
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@ -1078,15 +1078,23 @@ class lammps(object):
def extract_fix(self,fid,fstyle,ftype,nrow=0,ncol=0):
"""Retrieve data from a LAMMPS fix
This is a wrapper around the :cpp:func:`lammps_extract_fix`
function of the C-library interface.
This function returns ``None`` if either the fix id is not
recognized, or an invalid combination of :ref:`fstyle <py_style_constants>`
and :ref:`ftype <py_type_constants>` constants is used. The
names and functionality of the constants are the same as for
the corresponding C-library function. For requests to return
a scalar or a size, the value is returned, also when accessing
global vectors or arrays, otherwise a pointer.
This is a wrapper around the :cpp:func:`lammps_extract_fix` function
of the C-library interface. This function returns ``None`` if
either the fix id is not recognized, or an invalid combination of
:ref:`fstyle <py_style_constants>` and :ref:`ftype
<py_type_constants>` constants is used. The names and functionality
of the constants are the same as for the corresponding C-library
function. For requests to return a scalar or a size, the value is
returned, also when accessing global vectors or arrays, otherwise a
pointer.
.. note::
When requesting global data, the fix data can only be accessed
one item at a time without access to the whole vector or array.
Thus this function will always return a scalar. To access vector
or array elements the "nrow" and "ncol" arguments need to be set
accordingly (they default to 0).
:param fid: fix ID
:type fid: string