Tests

   (1) Compare individual forces and energies across different platforms
   (2) Check that individual forces and energies are consistent by perfroming
       the following sequence of steps:
 

           (i)    Compute the force (F0 = -grad_V|r = r0)  and potential energy (V0) for a
                  given configuration

           (ii)   Perturb the coordinates in the direction of the force F0 by an amount epsilon: 
	                   delta_r =  -F0*epsilon/ |F0|, where epsilon can range from 10-2 to 10-6 nm 

           (iii)  Calculate the potential energy V at the perturbed configuration
                     V               = V0 + (grad_V . delta_r) + ...
                     V - V0          = -F0 . delta_r = -F0(- epsilon*F0/|F0|) 
                     [V-V0]/epsilon  =   |F0|

    (3) Run tests for full systems to monitor energy drift for Verlet
        integrators and temperature stability for Langevin inegrators


Running tests:

    (1) Force and energy comparisons across platforms:

        pythcn ForceEnergyPlatformComparison.py -verbose 1 -controlFile EnergyConservationControlAll.txt

Configuration files used to externalize systems and tests:

    SystemNames.txt 
        list of system names to be used in tests; format is one system/line

    ForceEnergyComparisonTestNames.txt
        list of force and energy comparison tests; format is one test/line

    ForceEnergyGradientTestNames.txt
        list of force-energy gradfient ctests; format is one test/line

    EnergyConservationControlAll.txt
    EnergyConservationControlLimited.txt
    EnergyConservationTestNames.txt
    ForceEnergyControl.txt
    ForceEnergyGradientControl.txt
    ForceEnergyGradientTestNames.txt