;This function returns the extinction for a Fitzpatrick and Massa 
;extinction parameterization.  The input wavelength is in angstroms
;Started 7-24-96 by SRM

function fm,lam,x0,gam,c1,c2,c3,c4

x=10000./lam	;converts angstroms to mircons^-1
drude=(x^2)/((x^2-x0^2)^2+(gam*x)^2)
pol=0.5392*(x-5.9)^2+0.05644*(x-5.9)^3
smallx=where(x lt 5.9)

nsmall=n_elements(smallx)
if smallx(0) ne -1 then pol(smallx(0))=pol(smallx)*0.
fm=c1+c2*x+c3*drude+c4*pol
;window,6
goto,skipplot
plot,x,fm,yrange=[-4,25],xr=[5,12]
xyouts,max(x),max(fm),'fm'
oplot,x,c1+x*0.,color=50
xyouts,max(x),max(c1),'c1'

oplot,x,c2*x,color=100
xyouts,max(x),max(c2*x),'c2 (linear)'

oplot,x,c3*drude,color=150
xyouts,max(x),max(c3*drude),'c3 (drude)'


oplot,x,c4*pol,color=200
xyouts,max(x),max(c4*pol),'c4 (poly)'
skipplot:dum=0;print,'skipping plot'

return,fm
end