A tiny bugfix for the reset flag, and a brief explanation of the changes

doc/src/fix_ipi.txt

@@ -10,18 +10,19 @@ fix ipi command :h3
 
 [Syntax:]
 
-fix ID group-ID ipi address port \[unix\] :pre
+fix ID group-ID ipi address port \[unix\] \[reset\] :pre
 
 ID, group-ID are documented in "fix"_fix.html command
 ipi = style name of this fix command
 address = internet address (FQDN or IP), or UNIX socket name
 port = port number (ignored for UNIX sockets)
-optional keyword = {unix}, if present uses a unix socket :ul
+optional keyword = {unix}, if present uses a unix socket
+optional keyword = {reset}, if present reset electrostatics at each call :ul
 
 [Examples:]
 
 fix 1 all ipi my.server.com 12345
-fix 1 all ipi mysocket 666 unix
+fix 1 all ipi mysocket 666 unix reset
 
 [Description:]
 
@@ -57,6 +58,15 @@ input are listed in the same order as in the data file of LAMMPS. The
 initial configuration is ignored, as it will be substituted with the
 coordinates received from i-PI before forces are ever evaluated.
 
+A note of caution when using potentials that contain long-range 
+electrostatics, or that contain parameters that depend on box size:
+all of these options will be initialized based on the cell size in the
+LAMMPS-side initial configuration and kept constant during the run. 
+This is required to e.g. obtain reproducible and conserved forces. 
+If the cell varies too wildly, it may be advisable to reinitialize 
+these interactions at each call. This behavior can be requested by 
+setting the {reset} switch. 
+
 [Restart, fix_modify, output, run start/stop, minimize info:]
 
 There is no restart information associated with this fix, since all

src/USER-MISC/fix_ipi.cpp

@@ -195,7 +195,7 @@ FixIPI::FixIPI(LAMMPS *lmp, int narg, char **arg) :
   inet   = ((narg > 5) && (strcmp(arg[5],"unix") == 0) ) ? 0 : 1;
   master = (comm->me==0) ? 1 : 0;
   // check if forces should be reinitialized and set flag
-  reset_flag = ((narg > 6) || (strcmp(arg[5],"reset") == 0) ) ? 1 : 0;
+  reset_flag = ((narg > 6 && (strcmp(arg[5],"reset") == 0 )) || ((narg > 5) && (strcmp(arg[5],"reset") == 0)) ) ? 1 : 0;
 
   hasdata = bsize = 0;