MHTInitializeTrk:

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   Initialize the trk data structure. 
   This should be called by all custom scan-to-track functions to ensure 
   a uniform data structure for tracks.
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   Form:
   trk = MHTInitializeTrk( f )
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   ------
   Inputs
   ------
   f	  (.) Filter data structure, see KFInitialize

   -------
   Outputs
   -------
   trk	(.) Data structure
              .filter           Kalman filter data structure
              .mP         (x,1) Mean state prediction
              .pP         (x,x) Covariance prediction
              .m          (x,1) Mean state
              .p          (x,x) Covariance
              .meas       (1,:) Measurement indices
              .sensor     (1,:) Sensor indices
              .score      (1,1) Score
              .scoreTotal (1,1) Total score
              .treeID     (1,1) Tree ID of track
              .scanHist   (1,n) Scan index history
              .measHist   (1,n) Measurement index history
              .sensorHist (1,n) Sensor index history
              .mHist      (j,:) Full measurement history
              .tHist      (j,:) Time history
              .d          (1,m) MHT distance
              .new        
              .gate       (1,m) Gate booleans
              .tag        (1,1) Unique track tag
              .scan0      (1,1) Scan number at which this track is created

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