Error with "Fix external callback" while running simple.cpp example:

I get the following error after downloading the latest stable version and compiling it as a library:

aprun -n 2 ./a.out 2 in.lj
LAMMPS (5 Sep 2014)
Lattice spacing in x,y,z = 1.6796 1.6796 1.6796
Created orthogonal box = (0 0 0) to (6.71838 6.71838 6.71838)
1 by 1 by 2 MPI processor grid
Created 256 atoms
ERROR: Fix external callback function not set (…/fix_external.cpp:95)
Application 8161235 exit codes: 1
Application 8161235 resources: utime ~0s, stime ~0s, Rss ~6904, inblocks ~15536, outblocks ~38894

(aprun is a wrapper to run mpi code on a nersc/cray cluster)

I looked through the email lists and the source code but couldn’t figure out the problem.

Thank you for your help,

Just remove the “fix 2 external” line from simple/in.lj.

That example is not meant to use that fix or callbacks. I’m not

sure how that line got added. I think I was testing something
out at one point and must have left the line in,
and it accidentally got checked into the repo.

If you want to see an example that uses fix external

and callbacks, see COUPLE/lammps_quest.