pro ciret2_itercoef_retrieval2, dbz_layer, vdq_layer, temp_layer, dbz, vdq, ext_coeff, iwc, lambda, N0, $
am_regress,bm_regress,aa_regress,ba_regress

if float(temp_layer) ge 253. then pressure=50000.
if float(temp_layer) lt 253. then pressure=40000.
if float(temp_layer) lt 243. then pressure=30000.
if float(temp_layer) lt 233. then pressure=25000.
if float(temp_layer) lt 223. then pressure=20000.

rho_air=1.e-3*(pressure/(287.04*float(temp_layer)))

az=(0.19)*((6./(3.14159*0.92))^2)*((am_regress)^2)
bz=(2.*bm_regress)-6.
ab=(0.04394+0.06049)/2. & bb=(0.970+0.831)/2.

dyn_visc=(1.7e-5)*(10.)     ; the 1000/100 converts from kg/m*s to g/cm*s
kin_visc=dyn_visc/rho_air
g=981.


bv=(bb*(bm_regress+2.-ba_regress))-1.
av=ab*kin_visc*((2.*am_regress*g/(rho_air*(kin_visc^2)*aa_regress))^bb)

Z=(10.^((double(dbz)/10.d)))*1.d-12
Vdq=(double(vdq))


       ext_coeff=ext_coeff_expo_ZV_bvbzbm(Z, Vdq, double(bm_regress), double(bv),$
        double(bz), double(am_regress), double(av), double(az), double(rho_air))

       iwc=iwc_expo_ZV_bvbzbm(Z, Vdq, bm_regress, bv, bz, am_regress, av, az, ba_regress, rho_air)

       lambda=lambda_expo_ZV_bvbzbm(Z, Vdq,bm_regress, bv, bz, am_regress, av, az, ba_regress, rho_air)

       N0=iwc/(am_regress*bm_regress*(gamma(bm_regress))*(lambda^(-(bm_regress+1))))

return
end