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      SUBROUTINE slPREL (EP0, EP1, RMATP)

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      P R E L
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  Form the matrix of precession between two epochs, using the
  model of Simon et al (1994), which is suitable for long
  periods of time.

  (double precision)

  Given:
     EP0    dp         beginning epoch
     EP1    dp         ending epoch

  Returned:
     RMATP  dp(3,3)    precession matrix

  Notes:

     1)  The epochs are TDB Julian epochs.

     2)  The matrix is in the sense   V(EP1)  =  RMATP * V(EP0)

     3)  The absolute accuracy of the model is limited by the
         uncertainty in the general precession, about 0.3 arcsec per
         1000 years.  The remainder of the formulation provides a
         precision of 1 mas over the interval from 1000AD to 3000AD,
         0.1 arcsec from 1000BC to 5000AD and 1 arcsec from
         4000BC to 8000AD.

  Reference:
     Simon, J.L. et al., 1994. Astron.Astrophys., 282, 663-683.

  Called:  slDEUL

  P.T.Wallace   Starlink   23 August 1996

  Copyright (C) 1996 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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