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+.help pv2ue Jun99 "Slalib Package"
+.nf
+
+      SUBROUTINE slPVUE (PV, DATE, PMASS, U, JSTAT)
+
+     - - - - - -
+      P V U E
+     - - - - - -
+
+  Construct a universal element set based on an instantaneous position
+  and velocity.
+
+  Given:
+     PV        d(6)   heliocentric x,y,z,xdot,ydot,zdot of date,
+                      (AU,AU/s; Note 1)
+     DATE      d      date (TT Modified Julian Date = JD-2400000.5)
+     PMASS     d      mass of the planet (Sun=1; Note 2)
+
+  Returned:
+     U         d(13)  universal orbital elements (Note 3)
+
+                 (1)  combined mass (M+m)
+                 (2)  total energy of the orbit (alpha)
+                 (3)  reference (osculating) epoch (t0)
+               (4-6)  position at reference epoch (r0)
+               (7-9)  velocity at reference epoch (v0)
+                (10)  heliocentric distance at reference epoch
+                (11)  r0.v0
+                (12)  date (t)
+                (13)  universal eccentric anomaly (psi) of date, approx
+
+     JSTAT     i      status:  0 = OK
+                              -1 = illegal PMASS
+                              -2 = too close to Sun
+                              -3 = too slow
+
+  Notes
+
+  1  The PV 6-vector can be with respect to any chosen inertial frame,
+     and the resulting universal-element set will be with respect to
+     the same frame.  A common choice will be mean equator and ecliptic
+     of epoch J2000.
+
+  2  The mass, PMASS, is important only for the larger planets.  For
+     most purposes (e.g. asteroids) use 0D0.  Values less than zero
+     are illegal.
+
+  3  The "universal" elements are those which define the orbit for the
+     purposes of the method of universal variables (see reference).
+     They consist of the combined mass of the two bodies, an epoch,
+     and the position and velocity vectors (arbitrary reference frame)
+     at that epoch.  The parameter set used here includes also various
+     quantities that can, in fact, be derived from the other
+     information.  This approach is taken to avoiding unnecessary
+     computation and loss of accuracy.  The supplementary quantities
+     are (i) alpha, which is proportional to the total energy of the
+     orbit, (ii) the heliocentric distance at epoch, (iii) the
+     outwards component of the velocity at the given epoch, (iv) an
+     estimate of psi, the "universal eccentric anomaly" at a given
+     date and (v) that date.
+
+  Reference:  Everhart, E. & Pitkin, E.T., Am.J.Phys. 51, 712, 1983.
+
+  P.T.Wallace   Starlink   18 March 1999
+
+  Copyright (C) 1999 Rutherford Appleton Laboratory
+  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+
+.fi
+.endhelp