.. index:: fix nufeb/growth/simple

fix nufeb/growth/simple command
===============================

Syntax
""""""

.. parsed-literal::
    
     fix ID group-ID nufeb/growth/simple keyword value

* ID = user-assigned name for the fix
* group-ID = ID of the group atoms to apply the fix to
* keyword = *growth* 

	.. parsed-literal::
	
	    *growth* value = growth rate 

Examples
""""""""

.. code-block:: 

   group bac type 1
   
   fix f_simple bac nufeb/growth/simple growth 4e-4

Description
"""""""""""

Perform exponential microbial growth (or decay) to the atoms defined in *group-ID*. 
The fix is called at each biological step (see :doc:`run_style nufeb <run_style_nufeb>`)
to update atom attributes.
The following forward Euler method is implemented to update the mass (*m*) of each atom in the group:

.. math::

  m'= m + \mu \Delta t

  \hfill
  
where :math:`\mu` is the growth rate of the atoms (*growth*). 
The new mass is then used to update other atom attributes. For a coccus-style atom,
its diameter changes accordingly. For a bacillus-style atom, the update is along
the length of the atom while the variations in its width (diameter) are negligible.