add example to COUPLE folder demonstrating loading LAMMPS as a plugin.

examples/COUPLE/plugin/simple.c

@@ -0,0 +1,175 @@
+/* ----------------------------------------------------------------------
+   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
+   www.cs.sandia.gov/~sjplimp/lammps.html
+   Steve Plimpton, sjplimp@sandia.gov, Sandia National Laboratories
+
+   Copyright (2003) Sandia Corporation.  Under the terms of Contract
+   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
+   certain rights in this software.  This software is distributed under 
+   the GNU General Public License.
+
+   See the README file in the top-level LAMMPS directory.
+------------------------------------------------------------------------- */
+
+/* c_driver = simple example of how an umbrella program
+              can invoke LAMMPS as a library on some subset of procs
+   Syntax: simpleC P in.lammps
+           P = # of procs to run LAMMPS on
+               must be <= # of procs the driver code itself runs on
+           in.lammps = LAMMPS input script
+   See README for compilation instructions */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <mpi.h>
+#include "liblammpsplugin.h"  /* this is the include for the plugin loader */
+
+int main(int narg, char **arg)
+{
+  int n,me,nprocs;
+  int nprocs_lammps, lammps;
+  char line[1024];
+  MPI_Comm comm_lammps;
+  FILE *fp = NULL;
+  liblammpsplugin_t *plugin = NULL;
+  void *lmp = NULL;
+  double *x = NULL;
+  double *v = NULL;
+  char *strtwo;
+  char *cmds[2];
+  int *type = NULL;
+
+  /* setup MPI and various communicators
+     driver runs on all procs in MPI_COMM_WORLD
+     comm_lammps only has 1st P procs (could be all or any subset) */
+
+  MPI_Init(&narg,&arg);
+
+  if (narg != 4) {
+    printf("Syntax: simpleC P in.lammps /path/to/liblammps.so\n");
+    exit(1);
+  }
+
+  MPI_Comm_rank(MPI_COMM_WORLD,&me);
+  MPI_Comm_size(MPI_COMM_WORLD,&nprocs);
+
+  nprocs_lammps = atoi(arg[1]);
+  if (nprocs_lammps > nprocs) {
+    if (me == 0)
+      printf("ERROR: LAMMPS cannot use more procs than available\n");
+    MPI_Abort(MPI_COMM_WORLD,1);
+  }
+
+  if (me < nprocs_lammps) lammps = 1;
+  else lammps = MPI_UNDEFINED;
+  MPI_Comm_split(MPI_COMM_WORLD,lammps,0,&comm_lammps);
+
+  /* open LAMMPS input script */
+
+  if (me == 0) {
+    fp = fopen(arg[2],"r");
+    if (fp == NULL) {
+      printf("ERROR: Could not open LAMMPS input script\n");
+      MPI_Abort(MPI_COMM_WORLD,1);
+    }
+  }
+
+  /* run the input script thru LAMMPS one line at a time until end-of-file
+     driver proc 0 reads a line, Bcasts it to all procs
+     (could just send it to proc 0 of comm_lammps and let it Bcast)
+     all LAMMPS procs call lammps_command() on the line */
+
+  if (lammps == 1) {
+    plugin = liblammpsplugin_load(arg[3]);
+    if (plugin == NULL) {
+      if (me == 0) printf("ERROR: Could not load shared LAMMPS library\n");
+      MPI_Abort(MPI_COMM_WORLD,1);
+    }
+  }
+  if (lammps == 1) plugin->open(0,NULL,comm_lammps,&lmp);
+
+  while (1) {
+    if (me == 0) {
+      if (fgets(line,1024,fp) == NULL) n = 0;
+      else n = strlen(line) + 1;
+      if (n == 0) fclose(fp);
+    }
+    MPI_Bcast(&n,1,MPI_INT,0,MPI_COMM_WORLD);
+    if (n == 0) break;
+    MPI_Bcast(line,n,MPI_CHAR,0,MPI_COMM_WORLD);
+    if (lammps == 1) plugin->command(lmp,line);
+  }
+
+  /* run 10 more steps
+     get coords from LAMMPS
+     change coords of 1st atom
+     put coords back into LAMMPS
+     run a single step with changed coords */
+
+  if (lammps == 1) {
+    plugin->command(lmp,"run 10");
+
+    int natoms = plugin->get_natoms(lmp);
+    x = (double *) malloc(3*natoms*sizeof(double));
+    plugin->gather_atoms(lmp,"x",1,3,x);
+    v = (double *) malloc(3*natoms*sizeof(double));
+    plugin->gather_atoms(lmp,"v",1,3,v);
+    double epsilon = 0.1;
+    x[0] += epsilon;
+    plugin->scatter_atoms(lmp,"x",1,3,x);
+
+    plugin->command(lmp,"run 1");
+  }
+
+  // extract force on single atom two different ways
+
+  if (lammps == 1) {
+    double **f = (double **) plugin->extract_atom(lmp,"f");
+    printf("Force on 1 atom via extract_atom: %g\n",f[0][0]);
+
+    double *fx = (double *) plugin->extract_variable(lmp,"fx","all");
+    printf("Force on 1 atom via extract_variable: %g\n",fx[0]);
+  }
+
+  /* use commands_string() and commands_list() to invoke more commands */
+
+  strtwo = (char *)"run 10\nrun 20";
+  if (lammps == 1) plugin->commands_string(lmp,strtwo);
+
+  cmds[0] = (char *)"run 10";
+  cmds[1] = (char *)"run 20";
+  if (lammps == 1) plugin->commands_list(lmp,2,cmds);
+
+  /* delete all atoms
+     create_atoms() to create new ones with old coords, vels
+     initial thermo should be same as step 20 */
+
+  if (lammps == 1) {
+    int natoms = plugin->get_natoms(lmp);
+    type = (int *) malloc(natoms*sizeof(double));
+    int i;
+    for (i = 0; i < natoms; i++) type[i] = 1;
+
+    plugin->command(lmp,"delete_atoms group all");
+    plugin->create_atoms(lmp,natoms,NULL,type,x,v,NULL,0);
+    plugin->command(lmp,"run 10");
+  }
+
+  if (x) free(x);
+  if (v) free(v);
+  if (type) free(type);
+
+  // close down LAMMPS
+
+  if (lammps == 1) {
+    plugin->close(lmp);
+    liblammpsplugin_release(plugin);
+  }
+
+  /* close down MPI */
+
+  if (lammps == 1) MPI_Comm_free(&comm_lammps);
+  MPI_Barrier(MPI_COMM_WORLD);
+  MPI_Finalize();
+}