print warning about minimization energy with fix box/relax

doc/src/Section_errors.txt

@@ -11171,6 +11171,12 @@ Self-explanatory. :dd
 If the fix changes the timestep, the dump dcd file will not
 reflect the change. :dd
 
+{Energy due to X extra global DOFs will be included in minimizer energies} :dt
+
+When using fixes like box/relax, the potential energy used by the minimizer
+is augmented by an additional energy provided by the fix. Thus the printed
+converged energy may be different from the total potential energy. :dd
+
 {Energy tally does not account for 'zero yes'} :dt
 
 The energy removed by using the 'zero yes' flag is not accounted

src/min.cpp

@@ -187,6 +187,8 @@ void Min::setup(int flag)
             update->minimize_style);
     if (flag) {
       fprintf(screen,"  Unit style    : %s\n", update->unit_style);
+      fprintf(screen,"  Current step  : " BIGINT_FORMAT "\n",
+              update->ntimestep);
       timer->print_timeout(screen);
     }
   }
@@ -196,7 +198,12 @@ void Min::setup(int flag)
   // cannot be done in init() b/c update init() is before modify init()
 
   nextra_global = modify->min_dof();
-  if (nextra_global) fextra = new double[nextra_global];
+  if (nextra_global) {
+    fextra = new double[nextra_global];
+    if (comm->me == 0 && screen)
+      fprintf(screen,"WARNING: Energy due to %d extra global DOFs will"
+              " be included in minimizer energies\n",nextra_global);
+  }
 
   // compute for potential energy
 

src/min.h

@@ -123,6 +123,12 @@ Minimization requires that neigh_modify settings be delay = 0, every =
 changed them and will restore them to their original values after the
 minimization.
 
+W: Energy due to X extra global DOFs will be included in minimizer energies
+
+When using fixes like box/relax, the potential energy used by the minimizer
+is augmented by an additional energy provided by the fix. Thus the printed
+converged energy may be different from the total potential energy.
+
 E: Minimization could not find thermo_pe compute
 
 This compute is created by the thermo command.  It must have been