potential term to refine against chemical shift tensor magnitudes.

This term is normally constructed using the helper function 
<m cstMagTools>.create_CSTMagPot.

constructor: CSTMagPot(instanceName,
	               angle1Vals,
	               angle2Vals,
	               surf1Vals,
	               surf2Vals,
	               surf3Vals,
		       simulation=0)
  instanceName is a user-specified identifier
  angle1Vals and angle2Vals are sequences of angle values defining a grid
  on which three tensor magnitudes s11, s22 and s33 are specified.
  surf1Vals, surf2Vals and surf3Vals are these surface values in 
  <m cdsMatrix>.CDSMatrix_double objects.
  simulation is an optional <m simulation>.Simulation specification
  [it defaults to the current Simulation.]

methods
  addRestraints(restraintString) - add the specified restraints specified in 
                                   the given string. See below for restraint
                                   assignment syntax.

  calcEnergy()                 - calc energy, returns the energy value.
  calcEnergyAndDerivs(derivs)  - calc energy, derivs, returns the energy value.

  rms()            - return the restraint rms violation
  numRestraints()  - return the numbder of restraints defined for this term.
  violations()     - return number of violations
  restraints()     - return a list of restraints. See the description of the
		     CSTMag_Restraint class below.
  
  info()                    - current info about the state of this instance
  showRestraints(violated)  - return info on restraints. Argument violated is
                              boolean specifying whether to return only 
 			      violated restraints.
  showViolations()          - return string containing pretty-printed info
                              on all violated restraints.

  simulation()              - return the associated simulation.




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

  verbose    - if true, sporadically spit out info [False]
  scale      - scale factor [1]
  cstOffset  - offset added to all surfaces [0]
  cstScale   - scale factor applied to all surfaces [1]
  cstWeights - weighting in the energy calculation of each surface contribution
               [ (1,1,1) ]
  threshold  - threshold in violation calculation [0.5]
  showAllRestraints - boolean which changes the behavior of showViolations. If 
                      this parameter is set to True, the behavior of
		      showViolations is modified such that all restraints are
      	              printed. Violated restraints are indicated by an
                      asterisk in the first column. [False]

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

The following raw members can be accessed:

  angle1Vals          - values of angles on the grid
  angle2Vals            returned as a list.
  surf1               - the three surfaces representations corresponding to
  surf2                 s11, s22 and s33.
  surf3                 These are <m spline>.Spline2D objects.

 The energy function for each restraint is defined as

   scale * (w1 * (s11-s11_obs)^2 +
            w2 * (s22-s22_obs)^2 +
            w3 * (s33-s33_obs)^2 )

  where w1-3 are weights specified by cstWeights. s11, s22 and s33 are
calculated from the two associated dihedral phi1 and phi2 angles via

      s11 = cstScale * surf1(phi1,phi2) + cstOffset

surf1 is interpolated from the input surface grid values.
      
      
The restraint table format consists of pairs of specifications.

  NAME <string>

  ASSIgn (selection1A) (selection1B) (selection1C) (selection1D) 
         (selection2A) (selection2B) (selection2C) (selection2D) 
           <s11_obs> <s22_obs> <s33_obs>  ! optional comment

The name statement specifies the name for the following assignment. If
it is omitted, a numerical name is generated.

The two sets of four atom selections in the ASSIgn statement specify
two dihedral angles. This statement can be split across muliple lines,
but the comment, if specified, should be on the same line as s33_obs.


  CSTMag_Restraint class

methods:
  name()    - the restraint name
  comment() - the restraint comment (entered after the ! in the ASSIgn
              statement)
  energy()  - the energy associated with this restraint.

raw members:
  phi1    -    <m dihedral>.Dihedral objects representing the two 
  phi2         dihedral angles

  vphi1   -    values of these angles from the most recent energy calculation
  vphi2

  calcd1  -    calculated surface values
  calcd2
  calcd3

  obs1    -    observed surface values as input via the ASSIgn statement
  obs2         in the restraint table.
  obs3