-------------------------------------------------------------------------------
   Computes the cost functional for the Nelder-Meade algorithm 
   for least-squares attitude determination.
------------------------------------------------------------------------
   Form:
   J = CostNM( x, kX, S0, xA, lX )
-------------------------------------------------------------------------------

   ------
   Inputs
   ------
   x                      State
   kX                     Subindex for states to be used
   S0                     Inverse of initial state covariance
   xA                     Initial state
   lX                     Length of the state vector

   -------
   Outputs
   -------
   J                      Cost

-------------------------------------------------------------------------------