AIPS HELP file for TARS in 31DEC24

As of Sun Sep 8 19:42:29 2024

TARS: Faraday rotation synthesis on simulated input data

INPUTS

```INFILE                             Input file of the U,Q
dependence on frequency.
OUTFILE                            Output file of the depedence
on RM.
BLANK=>OUTFILE is not created
APARM                              Parameters for algorithm:
1 number of pixels at
half of the Fourier
transform output
The whole number is
2*APARM(1)+1
2 cell size in 1/m^2
0 =>
PI/(4*(Lmax^2-Lmin^2))
Lmax,Lmin-max,min lambda
at the data
3 0 => regular output
1 => output is RMTF
4 0=> CLEANed Fourier
transform
1=> unCLEANed Fourier
transform
5 0=>original(shifted back)
RE/IM are sent out
1=>the shifted RE/IM are
sent out
2=>amplitude and phase of
the data are sent out
6 Number of rows to use in
INFILE
0=> all rows in INFILE
7 0=> convolve the clean
components
1=> no convolve
8 0=> use the Gaussian as
the convolve function
1=> use the Re of RMTF as
the convolve function
9 full width of Gaussian
convolve function, at 0.5
level, in 1/m^2
0 => fit to real RMTF
< 0 => fit to amp RMTF
10 what send to output?
0 => sum of CLEAN and
residual
1 => CLEAN result
2 => residual
GAIN                               Gain in the CLEAN
NITER                              Maximum number of clean
components
FLUX                               Minimum flux of clean
component (Jy)
OPCODE                             'CMPL' - new method Clean
'ZERO' - no shift of lambda^2
else peak amplitude Clean
```

HELP SECTION

```TARS

(FARS)

INFILE......User-supplied text file giving Q (second column) and U
(third column) as a function of frequency (first
column).  A weight may be given in the fourth column.
These cards determine the frequecies that will be used
and their weights.  Default values for Q and U are 0
while the default weight is 1.

Model components (up to 20) may be added to the data
contained in the cards described above.   If the first
symbol is "M", then the following 3 numbers give the
parameters of a model component: RM, in 1/m^2; AMP, and
Phase in degrees.  The models are computed and added to
the data given in the main data cards --- if you want no
data added to the model, specify Q and U as 0.0 in the
data cards.

If the first symbol in a row is a semicolon, the row is
skipped and acts as a comment.  The format of columns in
INFILE is free with any number of blank characters
between columns.

The following is example of an INFILE with 2 components
in a model and 3 of the N rows of data

; Input file for TARS With the top rows for model.
; The model rows are started with symbol M
; and includes RM in 1/m^2,  AMP and PHASE in Degrees
;    RM, 1/m^2    AMP        Phase, deg
M     -600         5             60
M     -800         3              0
;  FREQ, Hz         Q               U        weight
1266000000     -3.6542873      -2.3332453      0.9
1276000000     -5.0204344      -1.8241444      1.0
1286000000     -4.3795457       0.393933       0.7

OUTFILE.....The result of calculation of Faraday rotation synthesis
is written to this file consist of 4 columns
1. the row number;
2. RM in 1/m^2
3. Amplitude (or Real, depending on APARM(5))
4. Phase (or Imaginary, depending on APARM(5))
' ' => results are directed to the message file and
message display
APARM.......Parameters: the same as in FARS
APARM(1) number of pixels at half of the Fourier
transform output.  The whole number is
2*APARM(1)+1 with zero at the center.
The value of APARM(1) should be chosen in
accordance of expected range of the Faraday
rotation measures and value of CELL (APARM(2))
APARM(2) cell size of the outputs, in 1/m^2.  The cell
is recomended to be less or around the default
value (pi)/4/(lambda^2max - lambda^2min)
APARM(3) 0 => regular outputs
1 => outputs are RMTF
APARM(4) 0=> CLEANed Fourier transform, using inputs:
NITER, FLUX, GAIN. The CLEAN uses the
shifed (at lambda^2) data but the cleaned
components correspond to the original lambda^2
RE is recorded to the first output
IM is recorded to the second output
1=> the uncleaned Fourier transform is recorded
RE is recorded to the first output
IM is recorded to the second output
APARM(5) 0=>original  data (RE and IM) are used at the
Fourier transform
1=> the shifted (to the center) data (RE, IM)
are used at the Fourier transform.
This option allows better discrimination
of different features at the Fourier transform.
2=> amplitude and phase of the data are sent out.
APARM(6) Number of rows to use in INFILE
0=> all rows in INFILE
If the first symbol at the infile row
.EQ. semicolumn, this row is skipped.
THIS SEICOLUMN CONCEPT CAN BE USED FOR SELECTION
THE ROWS!
APARM(7) 0=> convolve the clean components
1 => no convolve; So just the set of the clean
components is sent to the output files
No convolution is forced if:
uncleaned Fourier is sent out (APARM(4)=1)
APARM(8) 0=> use the Gaussian as the convolve function
1=> use the Re of RMTF as the convolve function
APARM(9) full width of the Gaussian convolve function,
at the 0.5 level, in 1/m^2.   0 -> fit the
real part of the RMTF.  -1 -> fit the amplitude
of the RMTF.  If OPCODE='ZERO' the amplitude
will be rather wider than the real part,
otherwise the two will be similar.
APARM(10) What send to the output?
0 => sum of CLEAN and  residual
1 => CLEAN result
2 => residual
GAIN........Gain in the CLEAN
NITER.......Maximum number of clean components 0 => 1
FLUX........Minimum Clean component (Jy)
The task can subtract the given number of complex
components. On each iteration, the maximum (and its
position) of the spectrum amplitude is determined.
The complex function RMTF is multiplied by the
complex value of the spectrum at the position of the
found amplitude maximum and by GAIN.
The found function(production) is put by its median
on the position of found amplitude maximum, and is
subtracted from the having evaluated spectrum. The
process of the subtraction is terminated having
achieved number of iterations NITER or the flux
FLUX.
OPCODE......'CMPL' invokes a (much slower) true complex Clean rather
than the one that looks for the peak in the
amplitude.  Does not seem to help.
'ZERO' turns of the shift of lambda^2 in the Fourier
transform.  The real part of the RMTF gets quite
a bit narrower, but the imaginary part becomes
significant.  Use APARM(9) < 0 to fit a more
reasonable restoring Gaussian.
other - standard peak in the amplitude Clean.
```

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