Comb News and Views

Changes for Comb 2000.0 

11. String lengths increased for BUNIT, TELESCOP, OBJECT
Formerly these FITS header variables were restricted to 8 characters.
That restriction is lifted. They can now be up to 68 characters
(as can any FITS string).

10. Dates now stored with stacks.

Previously, only scans had dates associated with them. With "st", the
date was lost. Now, the date of a scan is stored with the stack in
the j2sec variable (see news item #9).  The behavior of pd date: is
thus changed to print out the date in FITS format
(CCYY-MM-DDThh:mm:ss) of stack 1.  For stacks created in pre-2000.0
versions of comb, there will be no date stored with the stack
(.j2sec=0), so no date is printed out.  This same date string is
written out by "wf st:" in the DATE-OBS keyword. The creation date of
the file is written in the DATE keyword. Similarly, a FITS spectrum
with DATE-OBS defined has the equivalent value stored in j2sec.  All
output dates are UT.  Input dates are assumed to be UT.

9. New stack header variables j2sec and ftrm.

The number of seconds before or since J2000 is now stored 
in .j2sec.   Negative values of j2sec mean before J2000, positive
mean after J2000.  The value of j2sec is converted to calendar time
for spectral plots (pl).  Zero (2000-Jan-01 00:00:00UT) is ignored
since previous versions of the stack header have this location zeroed
out. So if you happen to take data at exactly 2000-Jan-01 00:00:00UT
it won't get displayed!  j2sec is set either from the J2Second
header variable (for Bell Labs format), from the Class3.ut variable
for NRAO format, or from the FITS DATE-OBS keyword for singledish
FITS format.  For co-added stacks (stacks with multiple scans), j2sec
has the value of that of the first scan in the list.

If Fourier components are removed from a stack (see ft ?! and News
item 3 below), the number of components removed is stored in .ftrm and
display in a spectral plot next to the baseline order.

These two variables took the part of the "spare" header variable 
isdum, which now down to the length of 2 short integers.

8. Baseline order FITS keyword for stacks 

The baseline order removed from a stack is now written out in 
FITS spectra (wf st:), using the keyword BASELN.  A value of -1 means 
no baseline has been removed.

7. New vertical offset option to "pl"

The plot command pl now has the option voff: to add an arbitrary vertical
offset to the current pl. This is useful for overlaying spectra without
having them right on top of each other. E.g

	-> rt 10;pl; rt 20; pl ovl:voff:3;rt 30; pl ovl:voff:-3

would plot stacks 20 and 30 over stack 10 with a vertical offsets of 3 
and -3, respectively, in the current plot units.  Note the offset can
be positive or negative and reverts to zero if not specified.

6. NRAO SDD and PDFL scans can now be read on little-endian machines (e.g, PCs).
At long last, Marc has made the NRAO scan routines working on PCs
(under Linux at least). 

5. Comb is Y2K compliant!

Actually there were only a few minor issues with Comb and the Year 2000.
The main one is that COMB now writes FITS files with the DATE value
according to the new FITS standard: CCYY-MM-DDThh:mm:ss in UT.

4. New predefined constants

For your convenience, AMU, C, E, G, K, MSUN, PC, and PI are now
predefined. You can access these as normal variables, eg.

	-> p .PI

For the exact definitions, see dv ?!.

3. Upgraded Fourier Transform (ft) command

The Fourier transform command ft has been upgraded by Tony Stark. New
features include removal of Fourier components and number of
components to fit.  (see also news item 9).

2. Stacks format change

The maximum number of channels allowed in comb is now 16224, down
from 16384 in previous versions.  This change was required because
the length of a stack index is limited to be a unsigned short integer
and must be a multiple of 32 for use arrays to work as defined.

1. 'up' (update search directory) and 'ns' (name stacks) upgraded

This was to fix a problem related to moving stacks files between
machines with different byte orders in their words.  (e.g. a PC and a
Sparcstation).  When opening stacks directories the files are now
checked for the correct byte order in a way which should work except
for some very unlikely cases.  'Ns' checks that the order is correct
and 'up' checks that it is wrong.  In either case if any errors are
found, the number of errors is printed as well as the number of
errors which would be found if the file were "up swap:"ed and the
user is asked to proceed.

In addition, 'up' has a new option, tbo:, to just test the byte order
and return. The same error report described above is given, but
no bytes are actually swapped. Use this if you aren't sure about
the origin of your stacks.

The documentation for 'up' ('up ?!') has been almost completely
rewritten.  The old version was useless and the new should be much
more helpful.