variable magnitude orientational tensor object

This object is usually constructed using the create_VarTensor() function in 
the <m varTensorTools> module. The VarTensor object is used by 
<m rdcPot>.RDCPot and <m csaPot>.CSAPot potential terms.

 The following parameters can be set [defaults in square brackets]

  Da        - axial tensor component. Setting this modifies ths position of 
              the p1 atom.
  Rh        - rhombic tensor component. Setting this modifies ths position of 
              the p2 atom.
  DaMax	    - maximum possible value of Da [50]
  verbose   - if true, sporadically spit out info [False]
  oAtom	    - origin atom
  o2Atom    - origin atom #2 (see below)
  xAtom	    - x-axis atom
  yAtom	    - y-axis atom
  zAtom	    - z-axis atom
  p1Atom    - Da parameter atom
  p2Atom    - rhombicity parameter atom
  potType   - type of potential: "harmonic" or "square" ["harmonic"]
  expts     - the potentials (RDCPots and CSAPots) which depend on this 
              tensor.
  freedom   - string used by varTensorTools.topologySetup to setup IVM
              topology.

 the above quantities may be retrieved using the member function form
 quantity(), while they are set using the form setQuantity(value).


if the associated Simulation object is an EnsembleSimulation, additional
functionality is available:

accessors:

  ensembleAxis - boolean. If true, there is a separate value for tensor
	         axis orientation for each ensemble member. True values
                 are not yet supported for refinement. Default is 0(false).
  ensembleDa - boolean. If true, there is a separate value of Da for 
               each structure. Default is 0(false).
  ensembleRh - boolean. If true, there is a separate value of rhombicity for 
               each structure. Default is 0(false).
  scaleDa    - weight on an energy term which weights spread in
               Da. This is only meaningful if ensembleDa is on. [default: 0]
  scaleRh    - weight on an energy term which weights spread in
               rhombicity. This is only meaningful if ensembleRh is on. 
               [default: 0]
  spreadDa   - Target spread in Da. Deviations in Da of less than
               spreadDa (from the mean) do not count towards the Da
               spread energy term. [default value: 0]
  spreadRh   - Target spread in rhombicity. Deviations in rhombicity
               of less than spreadRh (from the mean) do not count
               towards the rhombicity spread energy term. [default value: 0]

In addition the followiong methods are provided:

 aveDa()         - return the average value of Da
 aveRhombicity() - return the average value of rhombicity

The energy term associated with spread in Da and Rh is
     scaleDa * < harmonicSquare( Da - <Da> ) >
and
     scaleRh * < harmonicSquare( Rh - <Rh> ) >,
respectively.


 Implementation: required topology issues

 The VarTensor object is best used with the IVM module for coordinate
 minimization and manipulation. An example of such use is shown in the
 rdcPotTest.py script in the python/tests subdirectory. To exploit the full
 capabilities of the VarTensor object, seven atoms are used to represent
 tensor properties. A second origin atom (named OO2) is placed
 co-incident with atom OO. 

  The axial tensor component Da is represented as 
                    Da_max * cos(theta1)
 where theta1 is the angle defined by atomX-atomOO-atomPA1. The
 rhombic tensor component is represented by 
                    2/3 * sin(theta2)
 where theta2 is the angle defined by atomZ-atomOO2-atomPA2.