jump command

Syntax

jump file label
  • file = filename of new input script to switch to
  • label = optional label within file to jump to

Examples

jump newfile
jump in.run2 runloop
jump SELF runloop

Description

This command closes the current input script file, opens the file with the specified name, and begins reading LAMMPS commands from that file. Unlike the include command, the original file is not returned to, although by using multiple jump commands it is possible to chain from file to file or back to the original file.

If the word “SELF” is used for the filename, then the current input script is re-opened and read again.

Note

The SELF option is not guaranteed to work when the current input script is being read through stdin (standard input), e.g.

lmp_g++ < in.script

since the SELF option invokes the C-library rewind() call, which may not be supported for stdin on some systems or by some MPI implementations. This can be worked around by using the -in command-line switch, e.g.

lmp_g++ -in in.script

or by using the -var command-line switch to pass the script name as a variable to the input script. In the latter case, a variable called “fname” could be used in place of SELF, e.g.

lmp_g++ -var fname in.script < in.script

The 2nd argument to the jump command is optional. If specified, it is treated as a label and the new file is scanned (without executing commands) until the label is found, and commands are executed from that point forward. This can be used to loop over a portion of the input script, as in this example. These commands perform 10 runs, each of 10000 steps, and create 10 dump files named file.1, file.2, etc. The next command is used to exit the loop after 10 iterations. When the “a” variable has been incremented for the tenth time, it will cause the next jump command to be skipped.

variable a loop 10
label loop
dump 1 all atom 100 file.$a
run 10000
undump 1
next a
jump in.lj loop

If the jump file argument is a variable, the jump command can be used to cause different processor partitions to run different input scripts. In this example, LAMMPS is run on 40 processors, with 4 partitions of 10 procs each. An in.file containing the example variable and jump command will cause each partition to run a different simulation.

mpirun -np 40 lmp_ibm -partition 4x10 -in in.file

variable f world script.1 script.2 script.3 script.4
jump $f

Here is an example of a loop which checks every 1000 steps if the system temperature has reached a certain value, and if so, breaks out of the loop to finish the run. Note that any variable could be checked, so long as it is current on the timestep when the run completes. As explained on the variable doc page, this can be insured by including the variable in thermodynamic output.

variable myTemp equal temp
label loop
variable a loop 1000
run 1000
if "${myTemp} < 300.0" then "jump SELF break"
next a
jump SELF loop
label break
print "ALL DONE"

Here is an example of a double loop which uses the if and jump commands to break out of the inner loop when a condition is met, then continues iterating thru the outer loop.

label       loopa
variable    a loop 5
  label     loopb
  variable  b loop 5
  print     "A,B = $a,$b"
  run       10000
  if        "$b > 2" then "jump SELF break"
  next      b
  jump      in.script loopb
label       break
variable    b delete
next        a
jump        SELF loopa

Restrictions

If you jump to a file and it does not contain the specified label, LAMMPS will come to the end of the file and exit.