r.b. goldstein  march 1978
routine to set up uscor and calcor for propco
must only be called for the following values of ipct:
-2, 1, 2

this works via a series of pointer arrays, that point
to the following:
pxnudy:   external, neutral, time delay
pxchdy:   external, charged particle, time delay
pxnudo:   external, neutral, doppler
pxchdo:   external, charged particle, doppler
pinudy:   internal, neutral particle, time delay
pichdy:   internal, charged part., time delay
pinudo:   internal, neutral part., doppler
pichdo:   internal, charged part., doppler

the main loop for the "standard" logic is used for both
time delay and doppler and neutral and charged particle
corrections. it is made specific by changing the indices on
the arrays pint and pext which are equivalenced to the above
arrays.

each of the above pointer arrays is ordered so that the
"most desirable" correction type comes first. this order is
alterable by prplog in the case of active v.s. static
corrections.

internal corrections for doppler, tmdly, neutral and charged
particles. order determines desirability. the order is
alterable by prplog in the case of the active vs. the static
corrections.

*  start=500
-----------------------------------------------------------------------
"normal" logic
this code is only entered if there were no 3's set in the
10's digit of any jcal
it applies to both tmdly and dop according to "typ"
it applies to  charged particles, neutral atmosphere, and
planetary atmosphere, depending on ipart:
ipart:   1=neutral   2=charged   3=planet atm.

internal cals. once in this loop, there are no external
corrections. choose the most desirable internal correction
that is not shut off with a 1 in the 10's place
if it exists on tape, do not re-calculate it.