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1.1.3. System properties

This section documents the following functions:

• lammps_get_natoms()

• lammps_get_thermo()

• lammps_last_thermo()

• lammps_extract_box()

• lammps_reset_box()

• lammps_memory_usage()

• lammps_get_mpi_comm()

• lammps_extract_setting()

• lammps_extract_global_datatype()

• lammps_extract_global()

• lammps_extract_pair_dimension()

• lammps_extract_pair()

• lammps_map_atom()

---

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, changing values should be done with care. When accessing per-atom data, please note that these data are the per-processor local data and are indexed accordingly. Per-atom data can change sizes and ordering at every neighbor list rebuild or atom sort event as atoms migrate between subdomains and processors.

#include "library.h"
#include <stdio.h>

int main(int argc, char **argv)
{
  void *handle;
  int i;

  handle = lammps_open_no_mpi(0, NULL, NULL);
  lammps_file(handle,"in.sysinit");
  printf("Running a simulation with %g atoms.\n",
         lammps_get_natoms(handle));

  printf(" %d local and %d ghost atoms. %d atom types\n",
         lammps_extract_setting(handle,"nlocal"),
         lammps_extract_setting(handle,"nghost"),
         lammps_extract_setting(handle,"ntypes"));

  double  *dt = (double *)lammps_extract_global(handle,"dt");
  printf("Changing timestep from %g to 0.5\n", *dt);
  *dt = 0.5;

  lammps_command(handle,"run 1000 post no");

  for (i=0; i < 10; ++i) {
    lammps_command(handle,"run 100 pre no post no");
    printf("PE = %g\nKE = %g\n",
           lammps_get_thermo(handle,"pe"),
           lammps_get_thermo(handle,"ke"));
  }
  lammps_close(handle);
  return 0;
}

---

double lammps_get_natoms(void *handle)

---

double lammps_get_thermo(void *handle, const char *keyword)

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void *lammps_last_thermo(void *handle, const char *what, int index)

---

void lammps_extract_box(void *handle, double *boxlo, double *boxhi, double *xy, double *yz, double *xz, int *pflags, int *boxflag)

---

void lammps_reset_box(void *handle, double *boxlo, double *boxhi, double xy, double yz, double xz)

---

void lammps_memory_usage(void *handle, double *meminfo)

---

int lammps_get_mpi_comm(void *handle)

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int lammps_extract_setting(void *handle, const char *keyword)

---

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

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

---

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

---

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

---

int lammps_map_atom(void *handle, const void *id)