; Data from Steele and McEwen, 1990, Table 3.

r=[0.21,0.46,0.30]
dr=[0.10,0.10,0.07]
g=[2.20,2.56,5.15]
dg=[0.32,0.36,0.27]
e0=[3.4,1.8,3.1]
de0=[1.0,0.2,0.9]
rbyg=r/g
drbyg=rbyg*SQRT((dg/g)^2+(dr/r)^2)

s=sort(e0)
e0=e0(s)
de0=de0(s)
rbyg=rbyg(s)
drbyg=drbyg(s)

n=3
xr=[MIN(e0-de0),MAX(e0+de0)]
;yr=[MIN(rbyg-drbyg),MAX(rbyg+drbyg)]
yr=[0.0,0.5]
PLOT,e0,rbyg,PSYM=6,XRANGE=xr,YRANGE=yr $
	    ,XTITLE='Characteristic Energy (keV)' $
	    ,YTITLE='Red/Green Ratio' $
	    ,TITLE='Data from Steele & McEwen, JGR 95, p. 10329'
FOR i=0,n-1 DO BEGIN
    PLOTS,[e0(i),e0(i)],[rbyg(i)-drbyg(i),rbyg(i)+drbyg(i)]
    PLOTS,[e0(i)-de0(i),e0(i)+de0(i)],[rbyg(i),rbyg(i)]
    ENDFOR

yf=1
var=1
cur=svdfit(e0,rbyg,2,weight=1.0/drbyg,yfit=yf,variance=var)
;OPLOT,e0,yf
;PRINT,cur

yf2=1
var2=1
cur2=svdfit(e0,rbyg,2,weight=1.0/(drbyg+abs(cur(1))*de0),yfit=yf2,variance=var2)
nxr=!X.CRANGE
OPLOT,nxr,cur2(0)+cur2(1)*nxr,THICK=2
;OPLOT,e0,yf2,thick=2
PRINT,cur2

END