m.e.ash    july 1969    subroutine cpartl
interpolate for partials of coordinates from tape and calculate
partial of observations
itype indicates which body's partials to compute:
1-em, 2-mn, 3-pl, 4-sb, 5-sc, 6-pr, 7-er
11-19 are the planets' contributions to the SSBC offset
ngo = 1 calculate partial of coordinates only
ngo = 2 calculate partial of observation as well as partial
of coordinates
ngo = 3 calculate partial of coordinates only, but combine
the various contributions in DEREM, except when kick=3
kick= 1 radar or radio tracking observation
kick= 2 optical observation
kick= 3 transit or occultation observation
kick= 4 interferometer or pulsar observation

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arrays 'ivze' and 'ivus' indicate status of the partials arrays
derem,dermn,derpl,dersb,dersc -- ivze(i)= -1,0,1 if the
corresponding der** contains garbage, zeroes, or data.
ivus(i)= 0,1 if the corresponding der** is ignored or included
in cpartc calculations.
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partial derivatives of transit or occultation observation
input partials of 'logical coordinates' depends on ibtrn
first is the observed body relative to logical center
- - - assigned to dermn (1,2,3) or derpl (rest)
second is observer relative to logical center
- - - assigned to derem
for mutual mid-time events, second is dersc - second body rel.
to logical center
zero out garbage