add balance styles shift/report and rcb/report for reporting imbalances only

doc/src/fix_balance.rst

@@ -14,15 +14,15 @@ Syntax
 * balance = style name of this fix command
 * Nfreq = perform dynamic load balancing every this many steps
 * thresh = imbalance threshold that must be exceeded to perform a re-balance
-* style = *shift* or *rcb*
+* style = *shift* *shift/report* or *rcb* or *rcb/report*
 
   .. parsed-literal::
 
-       shift args = dimstr Niter stopthresh
+       *shift* or *shift/report* args = dimstr Niter stopthresh
          dimstr = sequence of letters containing *x* or *y* or *z*, each not more than once
          Niter = # of times to iterate within each dimension of dimstr sequence
          stopthresh = stop balancing when this imbalance threshold is reached
-       *rcb* args = none
+       *rcb* or *rcb/report* args = none
 
 * zero or more keyword/arg pairs may be appended
 * keyword = *weight* or *out*
@@ -70,6 +70,13 @@ re-balancing is performed periodically during the simulation.  To
 perform "static" balancing, before or between runs, see the
 :doc:`balance <balance>` command.
 
+.. versionadded:: TBD
+
+The *shift/report* and *rcb/report* styles only compute the
+load imbalance but do not attempt any re-balancing.  This way
+the load imbalance information can be used otherwise, for
+instance for stopping a run with :doc:`fix halt <fix_halt>`.
+
 Load-balancing is typically most useful if the particles in the
 simulation box have a spatially-varying density distribution or
 where the computational cost varies significantly between different

src/fix_balance.cpp

@@ -61,9 +61,18 @@ FixBalance::FixBalance(LAMMPS *lmp, int narg, char **arg) :
   if (nevery < 0) error->all(FLERR,"Illegal fix balance command");
   thresh = utils::numeric(FLERR,arg[4],false,lmp);
 
-  if (strcmp(arg[5],"shift") == 0) lbstyle = SHIFT;
-  else if (strcmp(arg[5],"rcb") == 0) lbstyle = BISECTION;
-  else error->all(FLERR,"Illegal fix balance command");
+  reportonly = 0;
+  if (strcmp(arg[5],"shift") == 0) {
+    lbstyle = SHIFT;
+  } else if (strcmp(arg[5],"shift/report") == 0) {
+    lbstyle = SHIFT;
+    reportonly = 1;
+  } else if (strcmp(arg[5],"rcb") == 0) {
+    lbstyle = BISECTION;
+  } else if (strcmp(arg[5],"rcb/report") == 0) {
+    lbstyle = BISECTION;
+    reportonly = 1;
+  } else error->all(FLERR,"Unknown fix balance style {}", arg[5]);
 
   int iarg = 5;
   if (lbstyle == SHIFT) {
@@ -75,7 +84,6 @@ FixBalance::FixBalance(LAMMPS *lmp, int narg, char **arg) :
     stopthresh = utils::numeric(FLERR,arg[iarg+3],false,lmp);
     if (stopthresh < 1.0) error->all(FLERR,"Illegal fix balance command");
     iarg += 4;
-
   } else if (lbstyle == BISECTION) {
     iarg++;
   }
@@ -175,7 +183,7 @@ void FixBalance::setup(int /*vflag*/)
 void FixBalance::setup_pre_exchange()
 {
   // do not allow rebalancing twice on same timestep
-  // even if wanted to, can mess up elapsed time in ImbalanceTime
+  // even if you wanted to, it can mess up elapsed time in ImbalanceTime
 
   if (update->ntimestep == lastbalance) return;
   lastbalance = update->ntimestep;
@@ -195,6 +203,7 @@ void FixBalance::setup_pre_exchange()
 
   balance->set_weights();
   imbnow = balance->imbalance_factor(maxloadperproc);
+
   if (imbnow > thresh) rebalance();
 
   // next timestep to rebalance
@@ -263,6 +272,13 @@ void FixBalance::pre_neighbor()
 
 void FixBalance::rebalance()
 {
+  // return immediately if only reporting of the imbalance is requested
+
+  if (reportonly) {
+    imbprev = imbfinal = imbnow;
+    return;
+  }
+  
   imbprev = imbnow;
 
   // invoke balancer and reset comm->uniform flag

src/fix_balance.h

@@ -45,6 +45,7 @@ class FixBalance : public Fix {
   std::string bstr;
   int wtflag;               // 1 for weighted balancing
   int sortflag;             // 1 for sorting comm messages
+  int reportonly;           // 1 if skipping rebalancing and only computing imbalance
 
   double imbnow;            // current imbalance factor
   double imbprev;           // imbalance factor before last rebalancing