update documentation

* adapt = style name of this fix command

* N = adapt simulation settings every this many timesteps

* one or more attribute/arg pairs may be appended

* attribute = *pair* or *kspace* or *atom*

* attribute = *pair* or *bond* or *kspace* or *atom*

  .. parsed-literal::

restart file written during a simulation will contain the modified

settings.

If the *scale* keyword is set to *no*\ , then the value the parameter is

set to will be whatever the variable generates.  If the *scale*

If the *scale* keyword is set to *no*\ , then the value of the altered

parameter will be whatever the variable generates.  If the *scale*

keyword is set to *yes*\ , then the value of the altered parameter will

be the initial value of that parameter multiplied by whatever the

variable generates.  I.e. the variable is now a "scale factor" applied

current list of atom parameters that can be varied by this fix:

* charge = charge on particle

* diameter = diameter of particle

* diameter, or, diameter/disc = diameter of particle

The *v\_name* argument of the *atom* keyword is the name of an

:doc:`equal-style variable <variable>` which will be evaluated each time

this fix is invoked to set the parameter to a new value.  It should be

specified as v\_name, where name is the variable name.  See the

this fix is invoked to set, or scale, the parameter to a new value.

It should be specified as v\_name, where name is the variable name.  See the

discussion above describing the formulas associated with equal-style

variables.  The new value is assigned to the corresponding attribute

for all atoms in the fix group.

.. note::

   The *atom* keyword works this way whether the *scale* keyword is

   set to *no* or *yes*\ .  I.e. the use of scale yes is not yet supported

   by the *atom* keyword.

If the atom parameter is *diameter* and per-atom density and per-atom

mass are defined for particles (e.g. :doc:`atom_style granular <atom_style>`), then the mass of each particle is also

changed when the diameter changes (density is assumed to stay

constant).

changed when the diameter changes. The mass is set from the particle volume

for 3d systems (density is assumed to stay constant). For 2d, the default is

for LAMMPS to model particles with a radius attribute as spheres.

However, if the atom parameter is *diameter/disc*, then the mass is

set from the particle area (the density is assumed to be in mass/distance^2 units).

For example, these commands would shrink the diameter of all granular

particles in the "center" group from 1.0 to 0.1 in a linear fashion