grompp: fix the -ref <file> option

Mark <file> optional (e.g. ffALLOW_MISSING).

A typical usage is
gmx grompp -ref rotref[.trr]
in which grompp will use rotref.0.trr, rotref.1.trr and so on,
but not rotref.trr. The easiest fix is hence to mark the file as optional.

Change-Id: Ide2947f57580b680d4f5f04ada22fd67d5fb0f93

diff --git a/src/gromacs/gmxpreprocess/grompp.cpp b/src/gromacs/gmxpreprocess/grompp.cpp
index f95384d1f818a9dc8f43428aab24462b175295b2..06185c4d4461dae33cb45e0e818f785b2fca415d 100644 (file)
--- a/src/gromacs/gmxpreprocess/grompp.cpp
+++ b/src/gromacs/gmxpreprocess/grompp.cpp
@@ -1789,7 +1789,7 @@ int gmx_grompp(int argc, char* argv[])
                        { efEDR, "-e", nullptr, ffOPTRD },
                        /* This group is needed by the VMD viewer as the start configuration for IMD sessions: */
                        { efGRO, "-imd", "imdgroup", ffOPTWR },
-                       { efTRN, "-ref", "rotref", ffOPTRW } };
+                       { efTRN, "-ref", "rotref", ffOPTRW | ffALLOW_MISSING } };
 #define NFILE asize(fnm)
 
     /* Command line options */