Merge pull request #1889 from lammps/change-box-error-check

.. note::

   The simulation box size/shape can be changed by arbitrarily

   large amounts by this command.  This is not a problem, except that the

   The simulation box size/shape can be changed by arbitrarily large

   amounts by this command.  This is not a problem, except that the

   mapping of processors to the simulation box is not changed from its

   initial 3d configuration; see the :doc:`processors <processors>`

   command.  Thus, if the box size/shape changes dramatically, the

   mapping of processors to the simulation box may not end up as optimal

   as the initial mapping attempted to be.

   mapping of processors to the simulation box may not end up as

   optimal as the initial mapping attempted to be.  You may wish to

   re-balance the atoms by using the :doc:`balance <balance>` command

   if that is the case.

.. note::

   Because the keywords used in this command are applied one at a

   time to the simulation box and the atoms in it, care must be taken

   with triclinic cells to avoid exceeding the limits on skew after each

   transformation in the sequence.  If skew is exceeded before the final

   transformation this can be avoided by changing the order of the

   sequence, or breaking the transformation into two or more smaller

   transformations.  For more information on the allowed limits for box

   skew see the discussion on triclinic boxes on :doc:`Howto triclinic <Howto_triclinic>` doc page.

   You cannot use this command after reading a restart file (and

   before a run is performed) if the restart file stored per-atom

   information from a fix and any of the specified keywords change the

   box size or shape or boundary conditions.  This is because atoms

   may be moved to new processors and the restart info will not

   migrate with them.  LAMMPS will generate an error if this could

   happen.  Only the *ortho* and *triclinic* keywords do not trigger

   this error.  One solution is to perform a "run 0" command before

   using the change_box command.  This clears the per-atom restart

   data, whether it has been re-assigned to a new fix or not.

.. note::

   Because the keywords used in this command are applied one at a time

   to the simulation box and the atoms in it, care must be taken with

   triclinic cells to avoid exceeding the limits on skew after each

   transformation in the sequence.  If skew is exceeded before the

   final transformation this can be avoided by changing the order of

   the sequence, or breaking the transformation into two or more

   smaller transformations.  For more information on the allowed

   limits for box skew see the discussion on triclinic boxes on

   :doc:`Howto triclinic <Howto_triclinic>` doc page.

----------

  if (domain->box_exist == 0)

    error->all(FLERR,"Change_box command before simulation box is defined");

  if (narg < 2) error->all(FLERR,"Illegal change_box command");

  if (modify->nfix_restart_peratom)

    error->all(FLERR,"Cannot change_box after "

               "reading restart file with per-atom info");

  if (comm->me == 0 && screen) fprintf(screen,"Changing box ...\n");

  if (nops == 0) error->all(FLERR,"Illegal change_box command");

  // move_atoms = 1 if need to move atoms to new procs after box changes

  // anything other than ORTHO or TRICLINIC may cause atom movement

  int move_atoms = 0;

  for (int m = 0; m < nops; m++) {

    if (ops[m].style != ORTHO || ops[m].style != TRICLINIC) move_atoms = 1;

  }

  // error if moving atoms and there is stored per-atom restart state

  // disallowed b/c restart per-atom fix info will not move with atoms

  if (move_atoms && modify->nfix_restart_peratom)

    error->all(FLERR,"Change_box parameter not allowed after "

               "reading restart file with per-atom info");

  // read options from end of input line

  options(narg-iarg,&arg[iarg]);

    if (domain->triclinic) domain->lamda2x(atom->nlocal);

  }

  // done if don't need to move atoms

  if (!move_atoms) return;

  // move atoms back inside simulation box and to new processors

  // use remap() instead of pbc()

  //   in case box moved a long distance relative to atoms