function wtn(q2_set)
	include ?

	real p1,p2,p3,p4,p5,p6,p7,p8,p9,p10,p11,p12
	real nsigl,nsigt,nsiglt,nsigtt
	real nsig219,nsig,wtn
	real ft,tav,ftav

	real pi,mtar_gev
	real my_limit
	integer q2_set
	parameter (pi=3.14159)
	parameter (mtar_gev=0.9395653)

	if (abs(q2_set-055).lt.1) then
	   p1=  0.58923E+03 
	   p2= -0.20500E+03 
	   p3= -0.28669E+02 
	   p4=  0.10000E+02 
	   p5=  0.00000E+00 
	   p6=  0.31777E+02 
	   p7=  0.19967E+02 
	   p8=  0.45000E+02 
	   p9= -0.20000E+03 
	   p10=-0.20000E+02 
	   p11= 0.00000E+00 
	   p12=-0.92659E+02 
	elseif (abs(q2_set-060).lt.1) then
	   p1=  0.42463E+03 
	   p2= -0.20500E+03 
	   p3= -0.19031E+02 
	   p4=  0.10000E+02 
	   p5=  0.00000E+00 
	   p6=  0.37387E+02 
	   p7= -0.20884E+02 
	   p8=  0.45000E+02 
	   p9= -0.20000E+03 
	   p10=-0.20000E+02 
	   p11= 0.00000E+00 
	   p12=-0.82691E+02 
	elseif (abs(q2_set-065).lt.1) then
	   p1=  0.27955E+03 
	   p2= -0.20500E+03 
	   p3= -0.11278E+02 
	   p4=  0.10000E+02 
	   p5=  0.00000E+00 
	   p6=  0.36616E+02 
	   p7= -0.58716E+02 
	   p8=  0.45000E+02 
	   p9= -0.20000E+03 
	   p10=-0.20000E+02 
	   p11= 0.00000E+00 
	   p12=-0.88789E+02 
	elseif (abs(q2_set-075).lt.1) then
	   p1=  0.42000E+03 
	   p2= -0.20500E+03 
	   p3= -0.16000E+02 
	   p4=  0.10000E+02 
	   p5=  0.00000E+00 
	   p6=  0.35000E+02 
	   p7= -0.50000E+02 
	   p8=  0.45000E+02 
	   p9= -0.20000E+03 
	   p10=-0.20000E+02 
	   p11= 0.00000E+00 
	   p12=-0.90000E+02
	elseif (abs(q2_set-100).lt.1) then
	   p1=  0.45848E+03 
	   p2= -0.20500E+03 
	   p3= -0.15782E+02 
	   p4=  0.10000E+02 
	   p5=  0.00000E+00 
	   p6=  0.35027E+02 
	   p7= -0.41985E+02 
	   p8=  0.45000E+02 
	   p9= -0.20000E+03 
	   p10=-0.20000E+02 
	   p11= 0.00000E+00 
	   p12=-0.94791E+02 
	elseif (abs(q2_set-160).lt.1) then
	   p1=  0.40022E+03 
	   p2= -0.20500E+03 
	   p3= -0.16163E+02 
	   p4=  0.10000E+02 
	   p5=  0.00000E+00 
	   p6=  0.35025E+02 
	   p7= -0.29050E+02 
	   p8=  0.45000E+02 
	   p9= -0.20000E+03 
	   p10=-0.20000E+02 
	   p11= 0.00000E+00 
	   p12=-0.39987E+02 
	else
	   write(*,*)'wtn: q2 error ',q2_set
	endif

***
* Cornel's parameterization
c	nsigl=(p1+p2*Q2i)*exp((p3+p4*Q2i)*ti)
c	nsigt=(p5+p6*Q2i)*exp((p7+p8*Q2i)*ti)
c
c	tmp=ti/(ti+0.02)**2
c	nsiglt=p9*exp(p10*ti)*sin(thetacmi) 
c	nsigtt=(p11/Q2i+p12/Q2i**2)*tmp*sin(thetacmi)**2 
c
* New parameterization suggested by Henk, 11.04.27
c	nsigl=(p1+p2*Q2i)*exp((p3+p4*log(Q2i))*ti)
c	nsigt=(p5/Q2i+p6/Q2i**2)*exp((p7+p8*log(Q2i))*ti)
c	nsiglt=p9*exp(p10*ti)*sin(thetacmi)
c
c	tmp=ti/(ti+0.02)**2
c	nsigtt=(p11/Q2i+p12/Q2i**2)*tmp*sin(thetacmi)**2
c
* Revised parameterization after IT11, 12.04.03
c	tmp=ti/(ti+0.139570**2)**2
c
c	nsigl=(p1+p2*log(Q2i))*exp((p3+p4*log(Q2i))*ti)
c	nsigt=p5+p6*log(Q2i)+(p7/Q2i**2+p8)*ti
c	nsiglt=p9*exp(p10*ti)*sin(thetacmi)
c	nsigtt=(p11/Q2i+p12/Q2i**2)*tmp*sin(thetacmi)**2
c
* Revised parameterization after IT19, 12.05.11
	ft=ti/(ti+0.139570**2)**2
        tav=(0.105+0.04*log(Q2i))*Q2i
        ftav=(ti-tav)/tav

c	nsigl=(p1+p2*log(Q2i))*exp((p3+p4*log(Q2i))*ti)
c	nsigt=p5+p6/Q2i**2+(p7+p8*log(Q2i))*ftav
c	nsiglt=p9*exp(p10*ti)*sin(thetacmi)
c	nsigtt=(p11/Q2i+p12/Q2i**2)*ft*sin(thetacmi)**2

* Minor Revisions after IT26, 12.05.19
	nsigl=(p1+p2*log(Q2i))*exp((p3+p4*log(Q2i))*ti)
	nsigt=p5+p6/(Q2i**2+0.10)+(p7+p8*log(Q2i))*ftav
	nsiglt=p9*exp(p10*ti)*sin(thetacmi)
	nsigtt=(p11/Q2i+p12/(Q2i**2+0.20))*ft*sin(thetacmi)**2

	nsig219=(nsigt+epsiloni*nsigl+epsiloni*cos(2.*phicmi)*nsigtt
     1      +sqrt(2.0*epsiloni*(1.+epsiloni))*cos(phicmi)*nsiglt)/1.d0

	wfactor=1.D0/(Wcmi**2-mtar_gev**2)**2
	nsig=nsig219*wfactor

	nsig=nsig/2./pi/1.d+06   !dsig/dtdphicm in microbarns/MeV**2/rad

	wtn=Weight*nsig/dsigdt

	my_limit=0.20
        if ((wtn.lt.my_limit).and.(wtn.gt.0.0)) then
          continue
        else
          wtn=0.
        endif

        return
	end