[daip] XINC in PRTUV

[Leonia Kogan]

Gustaaf,

I have not looked at the PRTUV's codes, but I am sure that
PRTUV select each XINC point from the data and then choose the
given baseline from the having selected data:

Prove:

The selected rows of the data for any given XINC are:

Isel = XINC*(I-1)+1

So XINC = 1 => Isel = 1,2,3...
    XINC = 2 => Isel = 1 3 5...
    XINC = 3 => Isel = 1 4 7..

The chosen baseline corresponds to the row numbers
Isel 43, 268, 693, 1018, 1343, 1668, 1993

XINC = 2 => the selected numbers must be odds that s why
             268, 1018 are skipped

XINC = 3 => the selected numbers minus 1 must devided by 3
             thats why 693, 1343, 1668.. are skipped
              but 43, 1018, 1993 are chosen


Gustaaf van Moorsel wrote:
> I find confusing behavior when using XINC in PRTUV.  I am selecting
> only baseline 13 - 16 using CPARM(9) = 1316.  The first visibility
> with that baseline is #43.
> 
> o XINC=1 lists visibilities #43, 268, 693, 1018, 1343, 1668, 1993,
>    as expected
> o XINC=2 lists visibilities #43, 693, 1343, as expected
> o XINC=3 lists visibilities #43, 1018, 1993, as expected
> o XINC=4 lists visibilities #693, 1993, etc.  Why not start with #43?
> o XINC=5 starts with #157666 !
> o XINC=6 lists visibilities #43, 1993, as expected
> o XINC=20 does not list any visibilities at all, whereas XINC=19 and
>    XINC=21 do (of which only the latter starts with #43)
> 
> If needed I'll be happy to make the data available.
> 
> Gustaaf
> 
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