git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@14073 f3b2605a-c512-4ea7-a41b-209d697bcdaa

examples/COUPLE/multiple/README

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+This directory has a C++ code multiple.cpp which illustrates how a
+driver code can create multiple instantiations of LAMMPS to run
+independent simulations simultaneously, on a set of processors
+allocated by MPI.
+
+Once you have built LAMMPS as a library (see examples/COUPLE/README),
+you can then build the driver codes with compile lines like these,
+which include paths to the LAMMPS library interface, MPI (an installed
+MPICH in this case), and FFTW (assuming you built LAMMPS as a library
+with its PPPM solver).
+
+g++ -I/home/sjplimp/lammps/src -c multiple.cpp
+g++ -L/home/sjplimp/lammps/src multiple.o \
+    -llammps -lfftw -lmpich -lmpl -lpthread -o multiple
+
+If you then run this command:
+
+% mpirun -np 8 multiple 4 in.chain 1.0 0.5
+
+you will create 4 instances of LAMMPS, each running on 2 of the
+allocated 8 processors.  The final two arguments are the base
+temperature and a delta temperature added by each instance.  The
+provided input script in.chain uses those temperatures, set as a
+variable "t" when each instance of LAMMPS is created.
+
+After a few seconds you should get this output to the screen:
+
+Instance 1, final temp = 1.00469
+Instance 2, final temp = 1.50395
+Instance 3, final temp = 1.99873
+Instance 4, final temp = 2.50862
+
+indicating the runs equilibrated to 4 temperatures separated by 0.5
+(in LJ units).  There should also be 4 screen files (screen.N) and 4
+log files (log.lammps.N) from the individual LAMMPS runs.

examples/COUPLE/multiple/in.chain

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+# FENE beadspring benchmark
+
+units		lj
+atom_style	bond
+special_bonds   fene
+
+read_data	data.chain
+
+neighbor	0.4 bin
+neigh_modify	every 1 delay 1
+
+bond_style      fene
+bond_coeff	1 30.0 1.5 1.0 1.0
+
+pair_style	lj/cut 1.12
+pair_modify	shift yes
+pair_coeff	1 1 1.0 1.0 1.12
+
+fix		1 all nve
+fix		2 all langevin $t $t 1.0 904297
+
+thermo          100
+timestep	0.012
+
+run		500

examples/COUPLE/multiple/multiple.cpp

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+/* ----------------------------------------------------------------------
+   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.
+------------------------------------------------------------------------- */
+
+// example of how a calling program can invoke
+//   multiple instances of LAMMPS, each on a subset of procs,
+//   and have each of them perform a different run, and collect output info
+// Syntax: mpirun -np P multiple N in.lammps T Tdelta
+//         P = # of total procs to run the driver program on
+//         N = # of instances of LAMMPS to create, P must be divisible by N
+//         in.lammps = LAMMPS input script,
+//                     which takes "t" as a temperature variable
+//         T = baseline temperature
+//         Tdelta = incremental temperature for each of N runs
+// See README for compilation instructions
+
+#include "stdio.h"
+#include "stdlib.h"
+#include "string.h"
+#include "mpi.h"
+
+#include "lammps.h"         // these are LAMMPS include files
+#include "input.h"
+#include "atom.h"
+#include "library.h"
+
+using namespace LAMMPS_NS;
+
+int main(int narg, char **arg)
+{
+  // 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 != 5) {
+    printf("Syntax: multiple N in.lammps T Tdelta\n");
+    exit(1);
+  }
+
+  int me,nprocs;
+  MPI_Comm_rank(MPI_COMM_WORLD,&me);
+  MPI_Comm_size(MPI_COMM_WORLD,&nprocs);
+
+  int ninstance = atoi(arg[1]);
+  if (nprocs % ninstance) {
+    if (me == 0)
+      printf("ERROR: Total procs must be divisble by N\n");
+    MPI_Abort(MPI_COMM_WORLD,1);
+  }
+
+  char *infile = arg[2];
+  double temperature = atof(arg[3]);
+  double tdelta = atof(arg[4]);
+
+  // create one communicator per instancem each with P/N procs
+
+  int instance = me*ninstance / nprocs;
+  MPI_Comm comm_lammps;
+  MPI_Comm_split(MPI_COMM_WORLD,instance,0,&comm_lammps);
+  
+  // each instance: unique screen file, log file, temperature
+
+  char str1[32],str2[32],str3[32];
+
+  char **lmparg = new char*[8];
+  lmparg[0] = NULL;                 // required placeholder for program name
+  lmparg[1] = (char *) "-screen";
+  sprintf(str1,"screen.%d",instance);
+  lmparg[2] = str1;
+  lmparg[3] = (char *) "-log";
+  sprintf(str2,"log.lammps.%d",instance);
+  lmparg[4] = str2;
+  lmparg[5] = (char *) "-var";
+  lmparg[6] = (char *) "t";
+  sprintf(str3,"%g",temperature + instance*tdelta);
+  lmparg[7] = str3;
+
+  // open N instances of LAMMPS
+  // either of these methods will work
+
+  LAMMPS *lmp = new LAMMPS(8,lmparg,comm_lammps);
+
+  //LAMMPS *lmp;
+  //lammps_open(8,lmparg,comm_lammps,(void **) &lmp);
+
+  delete [] lmparg;
+
+  // run input script thru all instances of LAMMPS
+
+  lammps_file(lmp,infile);
+
+  // query final temperature and print result for each instance
+
+  double *ptr = (double *) 
+    lammps_extract_compute(lmp,(char *) "thermo_temp",0,0);
+  double finaltemp = *ptr;
+
+  double *temps = new double[ninstance];
+  for (int i = 0; i < ninstance; i++) temps[i] = 0.0;
+
+  int me_lammps;
+  MPI_Comm_rank(comm_lammps,&me_lammps);
+  if (me_lammps == 0) temps[instance] = finaltemp;
+  
+  double *alltemps = new double[ninstance];
+  MPI_Allreduce(temps,alltemps,ninstance,MPI_DOUBLE,MPI_SUM,MPI_COMM_WORLD);
+
+  if (me == 0)
+    for (int i = 0; i < ninstance; i++)
+      printf("Instance %d, final temp = %g\n",i+1,alltemps[i]);
+
+  delete [] temps;
+  delete [] alltemps;
+
+  // delete LAMMPS instances
+
+  delete lmp;
+
+  // close down MPI
+
+  MPI_Comm_free(&comm_lammps);
+  MPI_Finalize();
+}