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updates to the fortran module docs to make it more consistent, fix links, add example similar to C library docs

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Axel Kohlmeyer
2022-09-23 12:41:31 -04:00
parent 2a14397318
commit d9e2be4b75
3 changed files with 142 additions and 74 deletions
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163
doc/src/Fortran.rst
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@ -3,7 +3,9 @@ The ``LIBLAMMPS`` Fortran Module
The ``LIBLAMMPS`` module provides an interface to call LAMMPS from a
Fortran code. It is based on the LAMMPS C-library interface and
requires a Fortran 2003 compatible compiler to be compiled.
requires a Fortran 2003 compatible compiler to be compiled. It is
designed to be self-contained and not require any support functions
written in C, C++, or Fortran.
While C libraries have a defined binary interface (ABI) and can thus be
used from multiple compiler versions from different vendors for as long
@ -19,12 +21,20 @@ for a simple program using the Fortran interface would be:
mpifort -o testlib.x lammps.f90 testlib.f90 -L. -llammps
Please note, that the MPI compiler wrapper is only required when the
calling the library from an MPI parallel code. Please also note the
order of the source files: the ``lammps.f90`` file needs to be compiled
first, since it provides the ``LIBLAMMPS`` module that is imported by
the Fortran code using the interface. A working example code can be
found together with equivalent examples in C and C++ in the
``examples/COUPLE/simple`` folder of the LAMMPS distribution.
calling the library from an MPI parallel code. Otherwise, using the
fortran compiler (gfortran, ifort, flang, etc.) will suffice. It may be
necessary to link to additional libraries depending on how LAMMPS was
configured and whether the LAMMPS library :doc:`was compiled as a static
or shared library <Build_link>`.
If the LAMMPS library itself has been compiled with MPI support, the
resulting executable will still be able to run LAMMPS in parallel with
``mpirun`` or equivalent. Please also note that the order of the source
files matters: the ``lammps.f90`` file needs to be compiled first, since
it provides the ``LIBLAMMPS`` module that is imported by the Fortran
code using the interface. A working example code can be found together
with equivalent examples in C and C++ in the ``examples/COUPLE/simple``
folder of the LAMMPS distribution.
.. versionadded:: 9Oct2020
@ -57,9 +67,10 @@ LIBLAMMPS`` statement. Internally it will call either
:cpp:func:`lammps_open_fortran` or :cpp:func:`lammps_open_no_mpi` from
the C library API to create the class instance. All arguments are
optional and :cpp:func:`lammps_mpi_init` will be called automatically,
if it is needed. Similarly, a possible call to :cpp:func:`lammps_finalize`
is integrated into the :f:func:`close` function and triggered with
the optional logical argument set to ``.true.``. Here is a simple example:
if it is needed. Similarly, a possible call to
:cpp:func:`lammps_mpi_finalize` is integrated into the :f:func:`close`
function and triggered with the optional logical argument set to
``.true.``. Here is a simple example:
.. code-block:: fortran
@ -81,8 +92,8 @@ the optional logical argument set to ``.true.``. Here is a simple example:
It is also possible to pass command line flags from Fortran to C/C++ and
thus make the resulting executable behave similarly to the standalone
executable (it will ignore the `-in/-i` flag, though). This allows one to
use the command line to configure accelerator and suffix settings,
executable (it will ignore the `-in/-i` flag, though). This allows
using the command line to configure accelerator and suffix settings,
configure screen and logfile output, or to set index style variables
from the command line and more. Here is a correspondingly adapted
version of the previous example:
@ -165,6 +176,57 @@ Below is a small demonstration of the uses of the different functions:
---------------
Accessing system properties
===========================
The C-library interface allows the :doc:`extraction of different kinds
of information <Library_properties>` about the active simulation
instance and also - in some cases - to apply modifications to it. In
some cases, the C-library interface makes pointers to internal data
structures accessible, thus when accessing them from Fortran, special
care is needed to avoid data corruption and crashes. Thus please see
the documentation of the individual type bound procedures for details.
Below is an example demonstrating some of the possible uses.
.. code-block:: fortran
PROGRAM testprop
USE LIBLAMMPS
USE, INTRINSIC :: ISO_C_BINDING, ONLY : c_double, c_int64_t
TYPE(lammps) :: lmp
INTEGER(kind=8) :: natoms
REAL(c_double), POINTER :: dt
INTEGER(c_int64_t), POINTER :: ntimestep
REAL(kind=8) :: pe, ke
lmp = lammps()
CALL lmp%file('in.sysinit')
natoms = INT(lmp%get_natoms(),8)
WRITE(6,'(A,I8,A)') 'Running a simulation with', natoms, ' atoms'
WRITE(6,'(I8,A,I8,A,I3,A)') lmp%extract_setting('nlocal'), ' local and', &
lmp%extract_setting('nghost'), ' ghost atom. ', &
lmp%extract_setting('ntypes'), ' atom types'
CALL lmp%command('run 2 post no')
dt = lmp%extract_global('dt')
ntimestep = lmp%extract_global('ntimestep')
WRITE(6,'(A,I4,A,F4.1,A)') 'At step:', ntimestep, ' Changing timestep from', dt, ' to 0.5'
dt = 0.5
CALL lmp%command('run 2 post no')
WRITE(6,'(A,I4)') 'At step:', ntimestep
pe = lmp%get_thermo('pe')
ke = lmp%get_thermo('ke')
PRINT*, 'PE = ', pe
PRINT*, 'KE = ', ke
CALL lmp%close(.TRUE.)
END PROGRAM testprop
---------------
The ``LIBLAMMPS`` module API
****************************
@ -292,7 +354,7 @@ Procedures Bound to the lammps Derived Type
This function will call :cpp:func:`lammps_get_natoms` and return the number
of atoms in the system.
:r real(C_double): number of atoms
:r real(c_double): number of atoms
--------
@ -302,16 +364,17 @@ Procedures Bound to the lammps Derived Type
of the corresponding thermodynamic keyword.
:p character(len=\*) name: string with the name of the thermo keyword
:r real(C_double): value of the requested thermo property or 0.0_C_double
:r real(c_double): value of the requested thermo property or `0.0_c_double`
--------
.. f:subroutine:: extract_box([boxlo][, boxhi][, xy][, yz][, xz][, pflags][, boxflag])
This subroutine will call :cpp:func:`lammps_extract_box`. All parameters
are optional, though obviously at least one should be present. The
parameters *pflags* and *boxflag* are stored in LAMMPS as integers, but
should be declared as ``LOGICAL`` variables when calling from Fortran.
This subroutine will call :cpp:func:`lammps_extract_box`. All
parameters are optional, though obviously at least one should be
present. The parameters *pflags* and *boxflag* are stored in LAMMPS
as integers, but should be declared as ``LOGICAL`` variables when
calling from Fortran.
:o real(c_double) boxlo [dimension(3),optional]: vector in which to store
lower-bounds of simulation box
@ -377,17 +440,18 @@ Procedures Bound to the lammps Derived Type
.. note::
The C library interface currently returns type "int" instead of type
"MPI_Fint", which is the C type corresponding to Fortran "INTEGER"
types of the default kind. On most compilers, these are the same anyway,
but this interface exchanges values this way to avoid warning messages.
The C library interface currently returns type ``int`` instead of
type ``MPI_Fint``, which is the C type corresponding to Fortran
``INTEGER`` types of the default kind. On most compilers, these
are the same anyway, but this interface exchanges values this way
to avoid warning messages.
.. note::
The MPI_F08 module, which defines Fortran 2008 bindings for MPI, is not
directly supported by this function. However, you should be able to
convert between the two using the MPI_VAL member of the communicator.
For example,
The `MPI_F08` module, which defines Fortran 2008 bindings for MPI,
is not directly supported by this function. However, you should be
able to convert between the two using the `MPI_VAL` member of the
communicator. For example,
.. code-block:: fortran
@ -398,14 +462,14 @@ Procedures Bound to the lammps Derived Type
! ... [commands to set up LAMMPS/etc.]
comm%MPI_VAL = lmp%get_mpi_comm()
should assign an MPI_F08 communicator properly.
should assign an `MPI_F08` communicator properly.
--------
.. f:function:: extract_setting(keyword)
Query LAMMPS about global settings. See the documentation for the
:c:func:`lammps_extract_setting` function from the C library.
:cpp:func:`lammps_extract_setting` function from the C library.
:p character(len=\*) keyword: string containing the name of the thermo keyword
:r integer(c_int): value of the queried setting or :math:`-1` if unknown
@ -414,35 +478,36 @@ Procedures Bound to the lammps Derived Type
.. f:function:: extract_global(name)
This function calls :c:func:`lammps_extract_global` and returns either a
string or a pointer to internal global LAMMPS data, depending on the data
requested through *name*.
This function calls :cpp:func:`lammps_extract_global` and returns
either a string or a pointer to internal global LAMMPS data,
depending on the data requested through *name*.
Note that this function actually does not return a value, but rather
associates the pointer on the left side of the assignment to point
to internal LAMMPS data (with the exception of string data, which are
copied and returned as ordinary Fortran strings). Pointers must be of the
correct data type to point to said data (typically INTEGER(c_int),
INTEGER(c_int64_t), or REAL(c_double)) and have compatible kind and rank.
The pointer being associated with LAMMPS data is type-, kind-, and
rank-checked at run-time via an overloaded assignment operator.
The pointers returned by this function are generally persistent; therefore
it is not necessary to call the function again, unless a :doc:`clear`
command has been issued, which wipes out and recreates the contents of
the :cpp:class:`LAMMPS <LAMMPS_NS::LAMMPS>` class.
associates the pointer on the left side of the assignment to point to
internal LAMMPS data (with the exception of string data, which are
copied and returned as ordinary Fortran strings). Pointers must be of
the correct data type to point to said data (typically
``INTEGER(c_int)``, ``INTEGER(c_int64_t)``, or ``REAL(c_double)``)
and have compatible kind and rank. The pointer being associated with
LAMMPS data is type-, kind-, and rank-checked at run-time via an
overloaded assignment operator. The pointers returned by this
function are generally persistent; therefore it is not necessary to
call the function again, unless a :doc:`clear` command has been
issued, which wipes out and recreates the contents of the
:cpp:class:`LAMMPS <LAMMPS_NS::LAMMPS>` class.
For example,
.. code-block:: fortran
PROGRAM demo
USE, INTRINSIC :: ISO_C_BINDING, ONLY : C_int64_t
USE, INTRINSIC :: ISO_C_BINDING, ONLY : c_int64_t
USE LIBLAMMPS
TYPE(lammps) :: lmp
INTEGER(C_int), POINTER :: nlocal
INTEGER(C_int64_t), POINTER :: ntimestep
INTEGER(c_int), POINTER :: nlocal
INTEGER(c_int64_t), POINTER :: ntimestep
CHARACTER(LEN=10) :: units
REAL(C_double), POINTER :: dt
REAL(c_double), POINTER :: dt
lmp = lammps()
! other commands
nlocal = lmp%extract_global('nlocal')
@ -457,7 +522,9 @@ Procedures Bound to the lammps Derived Type
the size of the current time step, and the units being used into the
variables *nlocal*, *ntimestep*, *dt*, and *units*, respectively.
*Note*: if this function returns a string, the string must have
.. note::
if this function returns a string, the string must have
length greater than or equal to the length of the string (not including the
terminal NULL character) that LAMMPS returns. If the variable's length is
too short, the string will be truncated. As usual in Fortran, strings
@ -469,7 +536,7 @@ Procedures Bound to the lammps Derived Type
pointer (e.g., ``INTEGER (c_int), POINTER :: nlocal``) to the extracted
property. If expecting vector data, the pointer should have dimension ":".
.. warning::
.. warning::
Modifying the data in the location pointed to by the returned pointer
may lead to inconsistent internal data and thus may cause failures or

30
doc/src/Library_properties.rst
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@ -15,21 +15,21 @@ This section documents the following functions:
--------------------
The library interface allows extraction of different kinds of
information about the active simulation instance and also
modifications to it. This enables combining of a LAMMPS simulation
with other processing and simulation methods computed by the calling
code, or by another code that is coupled to LAMMPS via the library
interface. In some cases the data returned is direct reference to the
original data inside LAMMPS, cast to a void pointer. In that case the
data needs to be cast to a suitable pointer for the calling program to
access it, and you may need to know the correct dimensions and
lengths. This also means you can directly change those value(s) from
the calling program, e.g. to modify atom positions. Of course, this
should be done with care. When accessing per-atom data, please note
that this data is the per-processor **local** data and is indexed
accordingly. Per-atom data can change sizes and ordering at every
neighbor list rebuild or atom sort event as atoms migrate between
The library interface allows the extraction of different kinds of
information about the active simulation instance and also - in some
cases - to apply modifications to it. This enables combining of a
LAMMPS simulation with other processing and simulation methods computed
by the calling code, or by another code that is coupled to LAMMPS via
the library interface. In some cases the data returned is direct
reference to the original data inside LAMMPS, cast to a void pointer.
In that case the data needs to be cast to a suitable pointer for the
calling program to access it, and you may need to know the correct
dimensions and lengths. This also means you can directly change those
value(s) from the calling program, e.g. to modify atom positions. Of
course, this should be done with care. When accessing per-atom data,
please note that this data is the per-processor **local** data and is
indexed accordingly. Per-atom data can change sizes and ordering at
every neighbor list rebuild or atom sort event as atoms migrate between
sub-domains and processors.
.. code-block:: C

1
doc/utils/sphinx-config/false_positives.txt
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@ -1094,6 +1094,7 @@ flagHI
flaglog
flagN
flagVF
flang
fld
floralwhite
Florez