YPF2T:

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   Converts years in fractional form, e.g. 1993.5 to T

   Since version 1.
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   Form:
   T = YPF2T( y )
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   ------
   Inputs
   ------
   y       (1,1) Year in fractional form

   -------
   Outputs
   -------
   T       (1,1) Julian centuries of 86400s dynamical time from j2000.0

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