pf - parabola fit
pf -3,15 see: Fit a parabola to stack 1 between -3 and 15 Km/s
(assuming horizontal plot units are velocity).
Put the parabola in stack1 and overlay the plot
of the present stack 1 with the parabola.
pf -3,14 rm: Fit and subtract a parabola between -3 and 15.
Pf fits a positive concave down parabola to the data in stack 1 over the
horizontal range given. The archetypical use of pf is in fitting the spectrum
of IRC+10216. The parameters of the fit are stored in the header variables
Unless the dp: flag is given, the parameters of the fit will be printed
on the terminal in horizontal plot units. A single header will be
printed for each command line.
See: first plots stack 1 if there is not a current plot, overwrites
stack 1 with the best fit parabola, and then overlays the parabola on
Rm: subtracts the fitted parabola from the stack, puts the residuals in
stack 1 and plots them.
Values returned by pf are which are stored in the stack header are
ftmax - peak temperature of fitted parabola
fterr - error in ftmax
fpeak - horizontal location of ftmax in plot units
fperr - error in fpeak
fwhm - fitted full width at half maximum in plot units
fwerr - error in fwhm
area - area of parabola in (K * plot units).
chisq - reduced chi-squared of the fit
nfree - number of free parameters (usually the number of channels - 2)
As usual, these are accessible via the "dot mechanism", e.g. 'p .fwhm'.
If the fit did not converge all the values are set to .DR.
See Bevington for a discussion of the fitting technique.
This document was last updated on
Tue Oct 17 16:24:05 EDT 2000
by Marc W. Pound.