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lhapdfif.f
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subroutine genericpdfset(ndns)
implicit none
include 'pwhg_pdf.h'
c wrap for pdfset; avoids subsequent
c calls to pdfset (you never know)
integer ndns
character * 20 parm(20)
real * 8 val(20)
integer ndns0
real * 8 genericxlambdL,genericxlambdNL,genericxlambdNNL,
, alphasPDF,asmz,mz,lam5
parameter (mz=91.1876d0)
integer iord
common/cgenericpdf/lam5,iord
real * 8 qcdl4,qcdl5
common/w50512/qcdl4,qcdl5
data ndns0/-1/
save ndns0
if(ndns.ne.ndns0) then
ndns0=ndns
parm(1)='DEFAULT'
val(1)=ndns
call pdfset(parm,val)
c find q2min and store it in common block
call GetQ2min(0,pdf_q2min)
c Workaround for lhapdf-6 bug:
c re-initialise the pdf set, since getq2min in lhapdf v6
c can change what was chosen with the first call to pdfset
ndns0=ndns
parm(1)='DEFAULT'
val(1)=ndns
call pdfset(parm,val)
asmz=alphasPDF(mz)
write(*,*) ' check: alpha_s(Mz)=',asmz
call GetOrderAs(iord)
if(iord.eq.0) then
c better to use the NLO formula anyhow;
c we don't have LO alpha around
lam5=genericxlambdNL(asmz,mz,5)
elseif(iord.eq.1) then
lam5=genericxlambdNL(asmz,mz,5)
elseif(iord.eq.2) then
lam5=genericxlambdNNL(asmz,mz,5)
endif
write(*,*) ' alpha_s order (0,1,2): ',iord
write(*,*) ' Lambda 5 is ',lam5
write(*,*) ' LHA value is ',qcdl5
c if(iord.lt.2) then
c write(*,*) ' alfa(mz):',alfas(mz**2,lam5,5)
c else
c write(*,*) ' alfa(mz):',alfa3(mz**2,lam5,5)
c endif
endif
end
function genericxlambdL(as,q,nf)
implicit none
real * 8 genericxlambdL,as,q
integer nf
real * 8 pi,b,t,xlt,ot,as0,as1
parameter (pi=3.14159265358979312D0)
b = (33-2*nf)/pi/12
t = 1/b/as
1 xlt = log(t)
ot = t
c-----------------------------------------------------------
c Value and Derivative of alfa with respect to t
as0 = 1/b/t
as1 = - 1/b/t**2
t = (as-as0)/as1 + t
if(abs(ot-t)/ot.gt.0.00000001d0)goto 1
genericxlambdL = q/exp(t/2)
return
end
function genericxlambdNL(as,q,nf)
implicit none
real * 8 genericxlambdNL,as,q
integer nf
real * 8 pi,b,bp,t,xlt,ot,as0,as1
parameter (pi=3.14159265358979312D0)
b = (33-2*nf)/pi/12
bp = (153 - 19*nf) / pi / 2 / (33 - 2*nf)
t = 1/b/as
1 xlt = log(t)
ot = t
c-----------------------------------------------------------
c Value and Derivative of alfa with respect to t
as0 = 1/b/t - bp*xlt/(b*t)**2
as1 = - 1/b/t**2 -bp/b**2*(1-2*xlt)/t**3
t = (as-as0)/as1 + t
if(abs(ot-t)/ot.gt.0.00000001d0)goto 1
genericxlambdNL = q/exp(t/2)
return
end
function genericxlambdNNL(as,q,nf)
implicit none
real * 8 genericxlambdNNL,as,q
integer nf
real * 8 pi,b0,b1,b2,t,xlt,ot,as0,as1
integer icount
parameter (pi=3.14159265358979312D0)
b0 = (33.d0-2.d0*nf)/(12.d0*pi)
b1 = (153.d0 - 19.d0*nf) / (24.d0*pi**2)
b2 = (2857.d0/2.d0-5033.d0/18.d0*nf+325.d0/54.d0*nf**2)
# /(4.d0*pi)**3
t = 1/b0/as
icount=0
1 xlt = log(t)
if(icount.gt.10000) then
write(*,*) ' xlambd: cannot converge '
stop
endif
icount=icount+1
ot = t
c-----------------------------------------------------------
c Value and Derivative of alfa with respect to t
as0 = 1/(t*b0)*(1-b1/b0**2*log(t)/t
# +(b1/b0**2*log(t)/t)**2
# -(b1**2*(log(t)+1)-b0*b2)/b0**4/t**2)
as1 =
5(-2*b1**2*log(t)**2/(b0**4*t**3)+2*(b1**2*(log(t)+1)-b0*b2)/(b0**4
1 *t**3)+b1*log(t)/(b0**2*t**2)+2*b1**2*log(t)/(b0**4*t**3)-b1/(b
2 0**2*t**2)-b1**2/(b0**4*t**3))/(b0*t)-(b1**2*log(t)**2/(b0**4*t
3 **2)-(b1**2*(log(t)+1)-b0*b2)/(b0**4*t**2)-b1*log(t)/(b0**2*t)+
4 1)/(b0*t**2)
t = (as-as0)/as1 + t
if(abs(ot-t)/ot.gt.0.00000001d0)goto 1
genericxlambdNNL = q/exp(t/2)
return
end
subroutine genericpdf(ndns,ih,xmu2,x,fx)
c Interface to lhapdf package.
implicit none
integer ndns,ih
real * 8 xmu2,x,fx(-6:6)
integer j
real * 8 tmp
call genericpdfset(ndns)
call evolvePDF(x,sqrt(xmu2),fx)
c pftopdg returns density times x
do j=-6,6
fx(j)=fx(j)/x
enddo
c 1 is proton, -1 is antiproton, 3 is pi+, -3 is pi-
if(ih.eq.1) then
return
elseif(ih.eq.-1) then
do j=1,6
tmp=fx(j)
fx(j)=fx(-j)
fx(-j)=tmp
enddo
c Do the neutron (Suggested by Jan Kretzschmar, 17/4/2013)
elseif(abs(ih).eq.2) then
c 2 is neutron: exchange u and d pdfs
tmp=fx(1)
fx(1)=fx(2)
fx(2)=tmp
tmp=fx(-1)
fx(-1)=fx(-2)
fx(-2)=tmp
if(ih.eq.-2) then
c -2 is anti-neutron: exchange quarks and anti-quarks, then u and d pdfs
do j=1,6
tmp=fx(j)
fx(j)=fx(-j)
fx(-j)=tmp
enddo
endif
elseif(ih.eq.3) then
tmp=fx(1)
fx(1)=fx(-1)
fx(-1)=tmp
elseif(ih.eq.-3) then
tmp=fx(2)
fx(2)=fx(-2)
fx(-2)=tmp
elseif(ih.eq.0) then
c 0 is deuteron
fx(1) = 0.5 * ( fx(1)+fx(2) )
fx(-1) = 0.5 * ( fx(-1)+fx(-2) )
fx(2) = fx(1)
fx(-2) = fx(-1)
elseif(ih.eq.4) then
c photon pdf
continue
else
write(*,*) ' genericpdf: unimplemented hadron type ',ih
stop
endif
c Bug fixes for version 5.3 of lhapdf
if(ndns.eq.363) then
do j=1,6
fx(j)=fx(j)/2
fx(-j)=fx(-j)/2
enddo
endif
end
subroutine genericpdfpar(ndns,ih,xlam,scheme,iorder,iret)
implicit none
integer ndns,ih,iorder
real * 8 xlam
character * 2 scheme
integer iret
real * 8 lam5
integer iord
common/cgenericpdf/lam5,iord
call genericpdfset(ndns)
scheme='MS'
iret=0
xlam=lam5
iorder=iord
end
function whichpdfpk()
character * 3 whichpdfpk
whichpdfpk='lha'
end