Basic Information on smavarfit

Task: smavarfit
Purpose: Analyse correlations of antenna gains and uv-variables.
Categories: uv analysis

SMAVARFIT is a Miriad task to analyse the correlations of
antenna gains and uv-variables rooted from the Miriad task
VARFIT. In addition to  fitting the following:
         yaxis = slope *  xaxis +  intercept
        D(yaxis) = slope * D(xaxis) + intercept
where D() is the difference between succesive samples,
SMAVARFIT provides an option of  regression for
the phases derived from the gains of two uvfiles.
If either axis is an antenna gain, then SELFCAL must be run first
and the axes are sampled at the interval used in SELFCAL.
The rms and correlation coefficient are listed for each antenna. 

Key: vis
The input UV dataset name. The antenna gains must first be
derived for the selected linetype by the task SELFCAL with
the desired averaging interval.

Key: xaxis
xaxis can be antenna gain ``amplitude'' or
``phase'', or any uv-variables. The default is ``time''.

Key: yaxis
yaxis can be antenna gain ``amplitude'' or
``phase'', or any uv-variables. The default is ``phase''.

Key: log
Output log file. Default is the terminal.

Key: device
Standard PGPLOT device, if plot of yaxis versus xaxis is wanted.
Default is no plot.

Key: nxy
Number of plots in the x and y directions. The default is 3,3.

Key: xrange
The min and max range along the x axis of the plots. The default
is to autoscale. Note that for "time" should be given in days.

Key: yrange
The min and max range along the y axis of the plots. The default
is to autoscale. Note that for "time" should be given in days.

Key: refant
Reference antenna for gains and uv-variables. If refant.ne.0 then
the gain of this antenna is set to cmplx(1.,0.). The
other antenna gains are then relative to the reference antenna.
The uv-variable value for the refant is subtracted from each of the
other antennas. Single valued variables, e.g. time, are unchanged.
The default is to use the original gains and uv-variable values.

Key: refant2
Reference antenna for cross correlation of gains and uv-variables.
Compare the gains or uv-variables between antennas by fitting
        yaxis = slope * xaxis(refant2) + intercept
       D(yaxis) = slope * D(xaxis(refant2)) + intercept
where D() is the difference between succesive samples.

Key: options
wrap         Do not unwrap phase.
xscale       Re-scale xaxis = slope * xaxis + offset, where slope
              and offset are fitted w.r.t. xaxis(refant)
              The fit is written into the log file. E.g.
              yaxis=phase xaxis=tpower refant=4 log=tpscale
              results can be used in the task tpgains to correct
              tpower to a common Tsys scale.
yscale       Re-scale yaxis = slope * yaxis + offset, where slope
              and offset are fitted w.r.t. yaxis(refant)
structure    Replace yaxis with it's structure function:
                <{yaxis(i+k) - yaxis(i)}**2>
allan        Replace yaxis with it's Allan variance:
                <{yaxis(i+2k) - 2*yaxis(i+k) + yaxis(i)}**2>
quad         Fit yaxis = a + b*xaxis + c*xaxis**2
              where a and b are first derived from a linear fit.
              The fit is written into the log file. E.g.
              yaxis=tpower xaxis=tpower refant2=4 options=quad
              results can be used in the task tpgains to correct
              tpower to a common Tsys scale.
phareg       do linear regression between phase1 and phase2 derived
             from the gain tables in uvfile1 and uvfile2, respectively:
             phase2 = slope * phase1 + offset

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