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   Finds the vectors
   rho   = z - h
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   Form:
   [rho, W, JL] = FXNM( x )
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   ------
   Inputs
   ------
   x         State vector

   -------
   Outputs
   -------
   rho       Residual vector z - h
   W         The measurement weighting vector
   JL        Cost eliminated by eliminating measurements
     
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