ERROR: Could not find undump ID

Dear LAMMPS-users,

During my simulation I want to dump and undump files. I implement the dump and undump command 9 times in my script, each time with exactly the same syntax, but a different dump ID. The code looks like this:

dump 1 all atom 50 dumpStep1.lammpstrj

dump_modify 1 sort id

run 1000000

undump 1


dump 2 all atom 50 dumpStep2.lammpstrj

dump_modify 2 sort id

run 1000000

undump 2


dump 3 all atom 50 dumpStep3.lammpstrj

dump_modify 3 sort id

run 1000000

undump 3


This implementation is used for all 9 dump and undump commands and it works fine for the first 7. However, somehow I get the message:

ERROR: Could not find undump ID <…/output.cpp:637>

Last command: undump 8

I’ve checked the syntax multiple times and I’ve looked for typos, but I can’t find any. It’s also clear that the corresponding “dump 8 …” command works fine, since i have a dump-file in my folder called dumpStep8.lammpstrj which is of normal file size (285,276 KB). What could be the reason for this error? Also, a few hours ago this “undump 8” command still worked fine.

Kind regards,


It will be easier if you share your whole input script or a reduced one that reproduces the issue. Otherwise it’s hard to say.