AIPS HELP file for MSORT in 31DEC24
As of Fri Apr 19 17:01:25 2024
MSORT: Task which sorts UV data
INPUTS
INNAME Input UV file name (name)
INCLASS Input UV file name (class)
INSEQ 0.0 9999.0 Input UV file name (seq. #)
INDISK Disk unit # of input UV data
OUTNAME Sorted UV file name (name)
OUTCLASS Sorted UV file name (class)
OUTSEQ -1.0 9999.0 Sorted UV file name (seq. #)
OUTDISK Disk unit # of sorted UV data
0 => highest with space
If outfile spec. equals the
infile spec., output will
overwrite the input
SORT Two char. sort order, eg.'TB'
blank => 'TB'
PRTLEV -1 -> no messages
0 -> major progress messages
1 -> show progress
HELP SECTION
MSORT
Type: Task
Use: To sort UV data into a specified order. Two keys are always
used in the sort.
This task differs from UVSRT in that no (large) scratch file is
required. It uses techniques that are very efficient in
sorting data that are nearly in the correct sort order. These
techniques degrade non-linearly as the sort problem becomes
worse - i.e. the visibility record size gets larger and the
average separation between the current record position and the
desired record position increases. For large records, MSORT
has a different brute-force disk-read sort that will work with
reasonable efficiency, but only if the input and output disk
files are not the same.
NOTE: this task does NOT apply flagging or calibration tables
to the input UV data. Run SPLIT first if that operation is
desired.
Adverbs:
INNAME.....Input UV file name (name). Standard defaults.
INCLASS....Input UV file name (class). Standard defaults.
INSEQ......Input UV file name (seq. #). 0 => highest.
INDISK.....Disk drive # of input UV. 0 => any.
OUTNAME....Output UV file name (name). Standard defaults.
OUTCLASS...Output UV file name (class). Standard defaults.
OUTSEQ.....Output UV file name (seq. #).0 = > highest unique.
OUTDISK....Disk drive # of output UV. 0 => highest with space
If the outfile specification equals the infile
specification, the output data file will overwrite
the input data file.
SORT.......Sort order of output. blank => 'TB' and is the
sort order needed for calibration routines
The sort order is specified by two keys which are
characters selected from:
blank => X = descending ABS(u)
B => baseline number
T => time order
U => u spatial freq. coordinate
V => v spatial freq. coordinate
W => w spatial freq. coordinate
R => baseline length.
P => baseline position angle.
X => descending ABS(u)
Y => descending ABS(v)
Z => ascending ABS(u)
M => ascending ABS(v)
see HELP SORT for more information
EXPLAIN SECTION
MSORT: Task which sorts UV data
DOCUMENTOR: K.M.Desai (NRAO/VLA)
RELATED PROGRAMS: UVSRT
PURPOSE
MSORT will sort a UV data base into a specified order. It is
almost functionally equivalent to UVSRT. The primary differences are
that UVSRT allows ROTATion of the U-V axes and that MSORT requires no
scratch disk space. The sorting operations are done in memory
resulting in a considerable speed up in execution time for certain
types of sorting problems.
This task is a heavy user of CPU power and memory.
COMMENTS
OUTNAME, OUTCLASS, OUTSEQ, OUTDISK:
If the outfile specification is identical to the infile
specification (including defaults used in both file specifications),
then the sorted data will overwrite the input data. Make sure the
input data set is properly backed up before you overwrite since a
computer crash may destroy the input data set.
TIMING:
Early testing results suggest that this program runs about
3 times faster when working on nearly sorted data and about 50 percent
slower when working on randomly sorted data as compared to
UVSRT.