diff -Naur lammps-5Sep09/doc/dump_modify.html lammps-6Sep09/doc/dump_modify.html --- lammps-5Sep09/doc/dump_modify.html 2009-09-02 14:56:46.000000000 -0600 +++ lammps-6Sep09/doc/dump_modify.html 2009-09-04 13:40:03.000000000 -0600 @@ -19,9 +19,10 @@
  • one or more keyword/value pairs may be appended -
  • keyword = every or flush or format or image or precision or region or scale or sort or thresh or unwrap +
  • keyword = append or every or flush or format or image or precision or region or scale or sort or thresh or unwrap -
      element args = E1 E2 ... EN, where N = # of atom types
+
      append arg = yes or no
+  element args = E1 E2 ... EN, where N = # of atom types
     E1,...,EN = element name, e.g. C or Fe or Ga
   every arg = N
     N = dump every this many timesteps
@@ -53,6 +54,17 @@
 
    Modify the parameters of a previously defined dump command.  Not all
 parameters are relevant to all dump styles.
 
    
+
    The append keyword applies to all dump styles except cfg and xtc
+and dcd.  It also applies only to text output files, not to binary
+or gzipped files.  If specified as yes, then dump snapshots are
+appended to the end of an existing dump file.  If specified as no,
+then a new dump file will be created which will overwrite an existing
+file with the same name.  This keyword can only take effect if the
+dump_modify command is used after the dump command, but
+before the first command that causes dump snapshots to be output,
+e.g. a run or minimize command.  Once the
+dump file has been opened, this keyword has no further effect.
+
    
 
    The element keyword applies only to the the dump cfg style.  It
 associates element names (e.g. H, C, Fe) with LAMMPS atom types, so
 that the AtomEye
@@ -146,7 +158,8 @@
 
    
 
    The option defaults are
 
    
-
    • element = "C" for every atom type
+
      • append = no
+
      • element = "C" for every atom type
 
      • every = whatever it was set to via the dump command
 
      • flush = yes (except for the dump xtc style)
 
      • format = %d and %g for each integer or floating point value
diff -Naur lammps-5Sep09/doc/dump_modify.txt lammps-6Sep09/doc/dump_modify.txt
--- lammps-5Sep09/doc/dump_modify.txt	2009-09-02 14:56:46.000000000 -0600
+++ lammps-6Sep09/doc/dump_modify.txt	2009-09-04 13:40:03.000000000 -0600
@@ -14,7 +14,8 @@
 
 dump-ID = ID of dump to modify :ulb,l
 one or more keyword/value pairs may be appended :l
-keyword = {every} or {flush} or {format} or {image} or {precision} or {region} or {scale} or {sort} or {thresh} or {unwrap} :l
+keyword = {append} or {every} or {flush} or {format} or {image} or {precision} or {region} or {scale} or {sort} or {thresh} or {unwrap} :l
+  {append} arg = {yes} or {no}
   {element} args = E1 E2 ... EN, where N = # of atom types
     E1,...,EN = element name, e.g. C or Fe or Ga
   {every} arg = N
@@ -46,6 +47,17 @@
 Modify the parameters of a previously defined dump command.  Not all
 parameters are relevant to all dump styles.
 
+The {append} keyword applies to all dump styles except {cfg} and {xtc}
+and {dcd}.  It also applies only to text output files, not to binary
+or gzipped files.  If specified as {yes}, then dump snapshots are
+appended to the end of an existing dump file.  If specified as {no},
+then a new dump file will be created which will overwrite an existing
+file with the same name.  This keyword can only take effect if the
+dump_modify command is used after the "dump"_dump.html command, but
+before the first command that causes dump snapshots to be output,
+e.g. a "run"_run.html or "minimize"_minimize.html command.  Once the
+dump file has been opened, this keyword has no further effect.
+
 The {element} keyword applies only to the the dump {cfg} style.  It
 associates element names (e.g. H, C, Fe) with LAMMPS atom types, so
 that the "AtomEye"_http://mt.seas.upenn.edu/Archive/Graphics/A
@@ -139,6 +151,7 @@
 
 The option defaults are
 
+append = no
 element = "C" for every atom type
 every = whatever it was set to via the "dump"_dump.html command
 flush = yes (except for the dump {xtc} style)
diff -Naur lammps-5Sep09/src/MOLECULE/dump_bond.cpp lammps-6Sep09/src/MOLECULE/dump_bond.cpp
--- lammps-5Sep09/src/MOLECULE/dump_bond.cpp	2008-04-08 07:58:15.000000000 -0600
+++ lammps-6Sep09/src/MOLECULE/dump_bond.cpp	2009-09-04 13:39:53.000000000 -0600
@@ -34,10 +34,6 @@
   int n = strlen(str) + 1;
   format_default = new char[n];
   strcpy(format_default,str);
-
-  // one-time file open
-
-  if (multifile == 0) openfile();
 }
 
 /* ---------------------------------------------------------------------- */
@@ -53,6 +49,10 @@
   format = new char[n];
   strcpy(format,str);
   strcat(format,"\n");
+
+  // open single file, one time only
+
+  if (multifile == 0) openfile();
 }
 
 /* ---------------------------------------------------------------------- */
diff -Naur lammps-5Sep09/src/dump.cpp lammps-6Sep09/src/dump.cpp
--- lammps-5Sep09/src/dump.cpp	2009-09-02 10:24:00.000000000 -0600
+++ lammps-6Sep09/src/dump.cpp	2009-09-04 13:39:53.000000000 -0600
@@ -53,6 +53,7 @@
   format_user = NULL;
 
   sort_flag = 0;
+  append_flag = 0;
 
   maxbuf = 0;
   buf = NULL;
@@ -65,6 +66,7 @@
   //   else if ends in .gz = gzipped text file
   //   else ASCII text file
 
+  singlefile_opened = 0;
   compressed = 0;
   binary = 0;
   multifile = 0;
@@ -233,7 +235,22 @@
 
   int iarg = 0;
   while (iarg < narg) {
-    if (strcmp(arg[iarg],"format") == 0) {
+    if (strcmp(arg[iarg],"append") == 0) {
+      if (iarg+2 > narg) error->all("Illegal dump_modify command");
+      if (strcmp(arg[iarg+1],"yes") == 0) append_flag = 1;
+      else if (strcmp(arg[iarg+1],"no") == 0) append_flag = 0;
+      else error->all("Illegal dump_modify command");
+      iarg += 2;
+    } else if (strcmp(arg[iarg],"every") == 0) {
+      if (iarg+2 > narg) error->all("Illegal dump_modify command");
+      int n = atoi(arg[iarg+1]);
+      if (n <= 0) error->all("Illegal dump_modify command");
+      int idump;
+      for (idump = 0; idump < output->ndump; idump++)
+	if (strcmp(id,output->dump[idump]->id) == 0) break;
+      output->dump_every[idump] = n;
+      iarg += 2;
+    } else if (strcmp(arg[iarg],"format") == 0) {
       if (iarg+2 > narg) error->all("Illegal dump_modify command");
       delete [] format_user;
       format_user = NULL;
@@ -249,15 +266,6 @@
       else if (strcmp(arg[iarg+1],"no") == 0) flush_flag = 0;
       else error->all("Illegal dump_modify command");
       iarg += 2;
-    } else if (strcmp(arg[iarg],"every") == 0) {
-      if (iarg+2 > narg) error->all("Illegal dump_modify command");
-      int n = atoi(arg[iarg+1]);
-      if (n <= 0) error->all("Illegal dump_modify command");
-      int idump;
-      for (idump = 0; idump < output->ndump; idump++)
-	if (strcmp(id,output->dump[idump]->id) == 0) break;
-      output->dump_every[idump] = n;
-      iarg += 2;
     } else if (strcmp(arg[iarg],"sort") == 0) {
       if (iarg+2 > narg) error->all("Illegal dump_modify command");
       if (strcmp(arg[iarg+1],"yes") == 0) sort_flag = 1;
@@ -290,6 +298,11 @@
 
 void Dump::openfile()
 {
+  // single file, already opened, so just return
+
+  if (singlefile_opened) return;
+  if (multifile == 0) singlefile_opened = 1;
+
   // if one file per timestep, replace '*' with current timestep
 
   char *filecurrent;
@@ -315,6 +328,8 @@
 #endif
     } else if (binary) {
       fp = fopen(filecurrent,"wb");
+    } else if (append_flag) {
+      fp = fopen(filecurrent,"a");
     } else {
       fp = fopen(filecurrent,"w");
     }
diff -Naur lammps-5Sep09/src/dump.h lammps-6Sep09/src/dump.h
--- lammps-5Sep09/src/dump.h	2009-09-02 10:24:00.000000000 -0600
+++ lammps-6Sep09/src/dump.h	2009-09-04 13:39:53.000000000 -0600
@@ -35,6 +35,8 @@
   int header_flag;           // 0 = item, 2 = xyz
   int flush_flag;            // 0 if no flush, 1 if flush every dump
   int sort_flag;             // 1 if write in sorted order, 0 if not
+  int append_flag;           // 1 if open file in append mode, 0 if not
+  int singlefile_opened;     // 1 = one big file, already opened, else 0
 
   char *format_default;      // default format string
   char *format_user;         // format string set by user
diff -Naur lammps-5Sep09/src/dump_atom.cpp lammps-6Sep09/src/dump_atom.cpp
--- lammps-5Sep09/src/dump_atom.cpp	2009-07-22 10:34:52.000000000 -0600
+++ lammps-6Sep09/src/dump_atom.cpp	2009-09-04 13:39:53.000000000 -0600
@@ -30,10 +30,6 @@
   scale_flag = 1;
   image_flag = 0;
   format_default = NULL;
-
-  // one-time file open
-
-  if (multifile == 0) openfile();
 }
 
 /* ---------------------------------------------------------------------- */
@@ -99,6 +95,10 @@
   if (binary) write_choice = &DumpAtom::write_binary;
   else if (image_flag == 0) write_choice = &DumpAtom::write_noimage;
   else if (image_flag == 1) write_choice = &DumpAtom::write_image;
+
+  // open single file, one time only
+
+  if (multifile == 0) openfile();
 }
 
 /* ---------------------------------------------------------------------- */
diff -Naur lammps-5Sep09/src/dump_custom.cpp lammps-6Sep09/src/dump_custom.cpp
--- lammps-5Sep09/src/dump_custom.cpp	2009-09-02 10:24:00.000000000 -0600
+++ lammps-6Sep09/src/dump_custom.cpp	2009-09-04 13:39:53.000000000 -0600
@@ -112,10 +112,6 @@
     strcat(columns,arg[iarg]);
     strcat(columns," ");
   }
-
-  // one-time file open
-
-  if (multifile == 0) openfile();
 }
 
 /* ---------------------------------------------------------------------- */
@@ -219,6 +215,10 @@
     if (ivariable < 0) error->all("Could not find dump custom variable name");
     variable[i] = ivariable;
   }
+
+  // open single file, one time only
+
+  if (multifile == 0) openfile();
 }
 
 /* ---------------------------------------------------------------------- */
diff -Naur lammps-5Sep09/src/dump_xyz.cpp lammps-6Sep09/src/dump_xyz.cpp
--- lammps-5Sep09/src/dump_xyz.cpp	2008-04-08 07:58:15.000000000 -0600
+++ lammps-6Sep09/src/dump_xyz.cpp	2009-09-04 13:39:53.000000000 -0600
@@ -45,9 +45,6 @@
     coords = (float *) memory->smalloc(3*natoms*sizeof(float),"dump:coords");
   }
 
-  // one-time file open
-
-  if (multifile == 0) openfile();
   ntotal = 0;
 }
 
@@ -74,6 +71,10 @@
   format = new char[n];
   strcpy(format,str);
   strcat(format,"\n");
+
+  // open single file, one time only
+
+  if (multifile == 0) openfile();
 }
 
 /* ----------------------------------------------------------------------