pro coma, r, a, f, pder
f = a(0)*exp(-r/a(1))*(a(2)+a(3)*r+r^2) + a(4)
pder = fltarr(n_elements(r), n_elements(a))
pder(*,0) = (f-a(4))/a(0)
pder(*,1) = (f-a(4))*r/a(1)^2
pder(*,2) = a(0)*exp(-r/a(1))
pder(*,3) = a(0)*exp(-r/a(1))*r
pder(*,4) = 1.0
return
end

	pro exptl, xx, vec, init
;fit an exponential and a parabola to a profile.
;"init" contains the initial guesses.
;the function is y = a(0)*exp(-x/a(1))*(a(2)+a(3)*x+x^2) + a(4)

resu = curvefit(xx, vec, findgen(n_elements(xx))*0.0+1.0, init, sigmaa, $
			function_name='coma', chi2=chi2)

	print, init
	return
	end