From fa080de7afc95aa1c19a6e6fc0e0708ced2eadc4 Mon Sep 17 00:00:00 2001
From: Joseph Hunkeler <jhunkeler@gmail.com>
Date: Wed, 8 Jul 2015 20:46:52 -0400
Subject: Initial commit

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 math/slalib/doc/pv2el.hlp | 145 ++++++++++++++++++++++++++++++++++++++++++++++
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+.help pv2el Jun99 "Slalib Package"
+.nf
+
+      SUBROUTINE slPVEL (PV, DATE, PMASS, JFORMR,
+     :                      JFORM, EPOCH, ORBINC, ANODE, PERIH,
+     :                      AORQ, E, AORL, DM, JSTAT)
+
+     - - - - - -
+      P V E L
+     - - - - - -
+
+  Heliocentric osculating elements obtained from instantaneous position
+  and velocity.
+
+  Given:
+     PV        d(6)   heliocentric x,y,z,xdot,ydot,zdot of date,
+                      J2000 equatorial triad (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)
+     JFORMR    i      requested element set (1-3; Note 3)
+
+  Returned:
+     JFORM     d      element set actually returned (1-3; Note 4)
+     EPOCH     d      epoch of elements (TT MJD)
+     ORBINC    d      inclination (radians)
+     ANODE     d      longitude of the ascending node (radians)
+     PERIH     d      longitude or argument of perihelion (radians)
+     AORQ      d      mean distance or perihelion distance (AU)
+     E         d      eccentricity
+     AORL      d      mean anomaly or longitude (radians, JFORM=1,2 only)
+     DM        d      daily motion (radians, JFORM=1 only)
+     JSTAT     i      status:  0 = OK
+                              -1 = illegal PMASS
+                              -2 = illegal JFORMR
+                              -3 = position/velocity out of range
+
+  Notes
+
+  1  The PV 6-vector is with respect to the mean equator and equinox of
+     epoch J2000.  The orbital elements produced are with respect to
+     the J2000 ecliptic and mean equinox.
+
+  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  Three different element-format options are supported:
+
+     Option JFORM=1, suitable for the major planets:
+
+     EPOCH  = epoch of elements (TT MJD)
+     ORBINC = inclination i (radians)
+     ANODE  = longitude of the ascending node, big omega (radians)
+     PERIH  = longitude of perihelion, curly pi (radians)
+     AORQ   = mean distance, a (AU)
+     E      = eccentricity, e
+     AORL   = mean longitude L (radians)
+     DM     = daily motion (radians)
+
+     Option JFORM=2, suitable for minor planets:
+
+     EPOCH  = epoch of elements (TT MJD)
+     ORBINC = inclination i (radians)
+     ANODE  = longitude of the ascending node, big omega (radians)
+     PERIH  = argument of perihelion, little omega (radians)
+     AORQ   = mean distance, a (AU)
+     E      = eccentricity, e
+     AORL   = mean anomaly M (radians)
+
+     Option JFORM=3, suitable for comets:
+
+     EPOCH  = epoch of perihelion (TT MJD)
+     ORBINC = inclination i (radians)
+     ANODE  = longitude of the ascending node, big omega (radians)
+     PERIH  = argument of perihelion, little omega (radians)
+     AORQ   = perihelion distance, q (AU)
+     E      = eccentricity, e
+
+  4  It may not be possible to generate elements in the form
+     requested through JFORMR.  The caller is notified of the form
+     of elements actually returned by means of the JFORM argument:
+
+      JFORMR   JFORM     meaning
+
+        1        1       OK - elements are in the requested format
+        1        2       never happens
+        1        3       orbit not elliptical
+
+        2        1       never happens
+        2        2       OK - elements are in the requested format
+        2        3       orbit not elliptical
+
+        3        1       never happens
+        3        2       never happens
+        3        3       OK - elements are in the requested format
+
+  5  The arguments returned for each value of JFORM (cf Note 5: JFORM
+     may not be the same as JFORMR) are as follows:
+
+         JFORM         1              2              3
+         EPOCH         t0             t0             T
+         ORBINC        i              i              i
+         ANODE         Omega          Omega          Omega
+         PERIH         curly pi       omega          omega
+         AORQ          a              a              q
+         E             e              e              e
+         AORL          L              M              -
+         DM            n              -              -
+
+     where:
+
+         t0           is the epoch of the elements (MJD, TT)
+         T              "    epoch of perihelion (MJD, TT)
+         i              "    inclination (radians)
+         Omega          "    longitude of the ascending node (radians)
+         curly pi       "    longitude of perihelion (radians)
+         omega          "    argument of perihelion (radians)
+         a              "    mean distance (AU)
+         q              "    perihelion distance (AU)
+         e              "    eccentricity
+         L              "    longitude (radians, 0-2pi)
+         M              "    mean anomaly (radians, 0-2pi)
+         n              "    daily motion (radians)
+         -             means no value is set
+
+  6  At very small inclinations, the longitude of the ascending node
+     ANODE becomes indeterminate and under some circumstances may be
+     set arbitrarily to zero.  Similarly, if the orbit is close to
+     circular, the true anomaly becomes indeterminate and under some
+     circumstances may be set arbitrarily to zero.  In such cases,
+     the other elements are automatically adjusted to compensate,
+     and so the elements remain a valid description of the orbit.
+
+  Reference:  Sterne, Theodore E., "An Introduction to Celestial
+              Mechanics", Interscience Publishers, 1960
+
+  Called:  slDA2P
+
+  P.T.Wallace   Starlink   13 February 1999
+
+  Copyright (C) 1999 Rutherford Appleton Laboratory
+  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+
+.fi
+.endhelp
-- 
cgit 

