the first card of the input data contains in columns 1 to 72 a
title for the program run read in a-format. the 72 characters of the
title appear at the top of every page of the printout and in the first
record of every data set generated by the program. the calendar date,
computed internally, also appears at the top of every printout page
and in the first record of every data set, so it is not necessary that
the date be included on the title card. the first eight characters of
the title card should be the run number because these first eight
characters alone are put in certain cells of the second record of the
output n-body tape.

next, there are cards read in subroutine input using namelist with
the title &nmlst1 giving the values of solar system and other
parameters.  the values on these cards may affect the form of the
rest of the input stream.  in particular, if jct(27) is set to 0
(the default), the input must conform to the rigid structure
described in the following paragraphs.  if jct(27) is set to 1, the
input must follow the '* command' format -- each group of input
cards must be preceded by a '*' card.  see below for details.

next, there is a sequence of sets of cards, each set read in
subroutine bodred using namelist with the title &nmlst2 and each set
giving the constants associated with the earth-moon barycenter
(nplnt=3), the moon (nplnt=10), the earth rotation (nplnt=-3),the moon
rotation (nplnt=-10), planets (nplnt=1,2,4,5,6,7,8,9 with ncentr=0),
asteroids (nplnt=11,...,30 with ncentr=0), natural satellites (nplnt=
11,...,30 with ncentr.gt.0), artificial space probes (nplnt.gt.30),
or planet rotation (nplnt=-1,-2,-4,...,-9,-11,...). the nplnt must
be distinct for each &nmlst2 if ict(1).ge.0. if ict(1)=-1, there can
be several &nmlst2 for each nplnt not equal to 3,10,-3,-10 to run
several integration test cases. also in certain test cases ncentr can
be -1 for nplnt=1,2,4,...,9,11,...,30. the &nmlst2 for planets which
are target or central bodies for satellite or probe integrations must
come before the &nmlst2 for the given satellite or probe. (note.
change in pep allows them to come after.)
the end of the sequence of &nmlst2 sets of cards is signaled by an
&nmlst2 set with nplnt=0.

note.... a fortran namelist restriction is that the '&' in front
of the namelist name start in column 2, that only columns 2-80 be
used in namelist, that a comma appear directly after each parameter
value, plus any other grammar mentioned in the fortran iv manual.
the last item in a namelist is &end.  it is recommended that columns
73-80 be left blank; peptic may someday be changed to ignore these
columns.

next, there are zero or more cards read in subroutine sitred
giving the coordinates of observing sites, with a maximum of 100
sites. there is one card per site, with an additional card giving the
radius and degree of flattening of the earth if geodetic coordinates
are input for which the radius and degree of flattening differ from
those input to pep as a whole. the end of the sequence of observing
site cards is signaled by a blank card.

next, there are zero or more cards read in subroutine sptred
giving the coordinates of spots on observed bodies and coordinates of
stars (body number negative), one card per spot or star with a
maximum of u_mxspt spots and stars. the end of the sequence of spot
and star cards is signaled by a blank card.

next, there are zero or more cards read in subroutine rbsred
giving constant biases for planetary radar observation series, one
card per series with a maximum of u_mxrbs series. the end of the
sequence of radar observation bias cards is signaled by a blank card.

next, there are zero or more cards read in subroutine eqnred
giving equinox-equator-latitude corrections for optical observation
series, one card per series with a maximum of 100 series. we are
thinking of adding additional optical observation series bias
corrections for refraction and position of observing site, which would
necessitate an additional card for each observation series. but for
the moment there is one card per series. the end of the sequence of
equinox-equator-latitude correction cards is signaled by a blank card.

next, there are zero or more cards read in subroutine phsred
giving planetary phase corrections for optical observation series, one
or two cards per series for each planet with a maximum of u_mxphs such
sets. the end of the sequence of phase correction cards is signaled
by a blank card.

next,    there are zero or more sets of cards read in subroutine
dltred controlling observation series changes, error weighting and
dummy observations. each set consists of a card describing the
observation series with exactly the same format as the card at the
start of the observation series on the observation card data set iobs
plus cards describing alterations in the
error weighting of individual observations or the generation of
specific dummy observations. the end of these additional cards is
signaled by a blank card and the end of the sequence of sets of cards
is signaled by a *end starting in column 1 (or by an end-of-file if
ict(42)=0, ict(44)=0, repeat=0 and no observations in input stream).

next, in subroutine filtin only if ict(42).ne.0.
if ict(42).eq.1,  &nmlst3  is read for controls for kalman filter
processing.  this is followed by the names of the process noise
parameters ending with a blank card.

in subroutine acmin only if ict(44) .ne.0
if ict(44).eq.1,  a title card  (80 cols.) followed by one or more
a priori input groups composed of an &nmlst4 followed by a priori
parameter name cards ending with a blank card.
&nmlst4 with n=0 ends the a priori input groups.
if ict(44).gt.1, these are read from data set no. = ict(44).

multin reads partial preduction requests (followed by one blank
card) (if jct(53).gt.0), and then multiple parameter set requests
(followed by one blank card) (if jct(51).gt.0). the blank card(s)
are included only if the associated jct(s) is (are).gt.0.

every parameter is given a standard value before the input cards
are read, so it is only necessary to read those parameters which
differ from their standard values. see the subroutines in which the
parameters are read to see the setup standard values and to see
definitions of the parameters.

ii &nmlst1
values of the control parameters used for program operati
and general solar system parameters.
explanation in subroutine prmred
&end

iii &nmlst2
nplnt=nonzero, plus values of data and control
constants for body nplnt
explanation in subroutine bodred
&end
....
....
....
sequence of such &nmlst2 namelists with nplnt=nonzero
....
....
....
&nmlst2
nplnt=0,
&end

vii equinox-equator-latitude corrections for optical observation
series
explanation in subroutine eqnred
one blank card

ix observation library series information
explanation in subroutine dltred
*end (or end of file if ict(42)=0, ict(44)=0, repeat=0 and no
observations in input stream)

x  &nmlst3  if ict(42).eq.1
controls for kalman filter processing
explanation in subroutine filtin
&end
followed by the names of the process noise parameters
explanation in subroutine filtin
one blank card

xii  heading  a priori title card (1 card 80 columns)
explanation in subroutine acmin
&nmlst4  if ict(44).eq.1
a priori values and covariances
explanation in subroutine acmin
&end
followed by the names of the a priori parameters
explanation in subroutine acmin and subroutine namprm
one blank card
....
....
sequence of such &nmlst4 namelists with n= non zero
followed by names of the a priori parameters  and
followed by one blank card
....
....
&nmlst4
n=0,
&end
one blank card

a dollar sign ($). pep does its own spooling and before a card
is given to the system namelist routines a search is made for a
$ sign and if one is found it and all the characters from that
point out to column 80 are blanked.

if jct(27).gt.0 then * command format of input required
restrictions on order in * command format
a. title card
b. &nmlst1
c. any *object packets
d. any other * commands
e. *apriori should come after most other input types
(because it produces summary of adj. params)
f. *multpar must follow *apriori
g. **end to end stream (or just end-of-file)
h. all namelist control cards should be omitted except
&nmlst1 and the &nmlst4/&end cards for a priori input.
also, the blank card separators should be omitted
except in the midst of a priori input.

this is the list of plnt names allowed on the *object card. the
corresponding planet number is in the array bn. 22 planets are
currently allowed by name. any plnt nmbr can be specified by using
*object ######## where # is the planet #.

read a priori title card, a priori input
groups (&nmlst4 followed by a priori parameter name cards)
acmin requires that initializations for all routines
have been done before it is called