add 'append' keyword for appending to output file

doc/src/fix_ave_chunk.rst

@@ -31,7 +31,7 @@ Syntax
        v_name = per-atom vector calculated by an atom-style variable with name
 
 * zero or more keyword/arg pairs may be appended
-* keyword = *norm* or *ave* or *bias* or *adof* or *cdof* or *file* or *overwrite* or *format* or *title1* or *title2* or *title3*
+* keyword = *norm* or *ave* or *bias* or *adof* or *cdof* or *file* or *append* or *overwrite* or *format* or *title1* or *title2* or *title3*
 
   .. parsed-literal::
 
@@ -51,6 +51,8 @@ Syntax
          dof_per_chunk = define this many degrees-of-freedom per chunk for temperature calculation
        *file* arg = filename
          filename = file to write results to
+       *append* arg = filename
+         filename = file to append results to
        *overwrite* arg = none = overwrite output file with only latest output
        *format* arg = string
          string = C-style format string
@@ -433,15 +435,21 @@ molecule.
 
 ----------
 
-The *file* keyword allows a filename to be specified.  Every
-:math:`N_\text{freq}` timesteps, a section of chunk info will be written to a
-text file in the following format.  A line with the timestep and number of
-chunks is written.  Then one line per chunk is written, containing the chunk
-ID :math:`(1-N_\text{chunk}),` an optional original ID value, optional
-coordinate values for chunks that represent spatial bins, the number of atoms
-in the chunk, and one or more calculated values.  More explanation of the
-optional values is given below.  The number of values in each line
-corresponds to the number of values specified in the fix ave/chunk
+.. versionadded:: TBD
+   new keyword *append*
+
+The *file* or *append* keywords allow a filename to be specified.  If
+*file* is used, then the filename is overwritten if it already exists.
+If *append* is used, then the filename is appended to if it already
+exists, or created if it does not exist.  Every :math:`N_\text{freq}`
+timesteps, a section of chunk info will be written to a text file in the
+following format.  A line with the timestep and number of chunks is
+written.  Then one line per chunk is written, containing the chunk ID
+:math:`(1-N_\text{chunk}),` an optional original ID value, optional
+coordinate values for chunks that represent spatial bins, the number of
+atoms in the chunk, and one or more calculated values.  More explanation
+of the optional values is given below.  The number of values in each
+line corresponds to the number of values specified in the fix ave/chunk
 command.  The number of atoms and the value(s) are summed or average
 quantities, as explained above.
 

doc/src/fix_ave_histo.rst

@@ -46,7 +46,7 @@ Syntax
        *file* arg = filename
          filename = name of file to output histogram(s) to
        *append* arg = filename
-         filename = name of file to append time averages to
+         filename = name of file to append histogram(s) to
        *ave* args = *one* or *running* or *window*
          one = output a new average value every Nfreq steps
          running = output cumulative average of all previous Nfreq steps

src/fix_ave_chunk.cpp

@@ -193,10 +193,12 @@ FixAveChunk::FixAveChunk(LAMMPS *lmp, int narg, char **arg) :
       cdof = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
 
-    } else if (strcmp(arg[iarg],"file") == 0) {
-      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "fix ave/chunk file", error);
+    } else if ((strcmp(arg[iarg],"file") == 0) || (strcmp(arg[iarg],"append") == 0)) {
+      if (iarg+2 > narg)
+        utils::missing_cmd_args(FLERR, std::string("fix ave/chunk ")+arg[iarg], error);
       if (comm->me == 0) {
-        fp = fopen(arg[iarg+1],"w");
+        if (strcmp(arg[iarg],"file") == 0) fp = fopen(arg[iarg+1],"w");
+        else fp = fopen(arg[iarg+1],"a");
         if (fp == nullptr)
           error->one(FLERR, "Cannot open fix ave/chunk file {}: {}",
                      arg[iarg+1], utils::getsyserror());