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! -*- F90 -*-
!-------------------------------------------------------------------
!-- Example program to demonstrate usage of the MSTW 2008 PDFs. --
!-- LHAPDF version by Graeme Watt <watt(at)hep.ucl.ac.uk>. --
!-------------------------------------------------------------------
PROGRAM Example8
IMPLICIT NONE
INTEGER iset,ieigen,neigen,ix,nx,iq,nq,flav,nhess
DOUBLE PRECISION x,q,xmin,xmax,q2min,q2max, &
& xf(-6:6),xfp(-6:6),xfm(-6:6), &
& summin(-6:6),summax(-6:6),sum(-6:6), &
& mCharm,mBottom,qcdl4,qcdl5,alphasPDF,MZ
CHARACTER flavours(-5:5)*10,xfilename(-5:5)*50,qfilename(-5:5)*50
DATA flavours /"bbar","cbar","sbar","ubar","dbar","glu", &
& "dn","up","str","chm","bot"/
call SetLHAPARM('EXTRAPOLATE') ! extrapolate beyond grids
!-- Two sets of error PDFs are provided for each fit, corresponding to
!-- an estimated 90% C.L. (as for previous MRST and CTEQ sets) or to
!-- a 68% (one-sigma) C.L.: see Section 6 of arXiv:0901.0002.
!-- The central PDF set is the same in both cases.
call InitPDFSetByNameM(1,"MSTW2008lo90cl.LHgrid") ! 90% C.L.
call InitPDFSetByNameM(2,"MSTW2008nlo90cl.LHgrid") ! 90% C.L.
call InitPDFSetByNameM(3,"MSTW2008nnlo90cl.LHgrid") ! 90% C.L.
!call InitPDFSetByNameM(1, "MSTW2008lo68cl.LHgrid") ! 68% C.L.
!call InitPDFSetByNameM(2, "MSTW2008nlo68cl.LHgrid") ! 68% C.L.
!call InitPDFSetByNameM(3, "MSTW2008nnlo68cl.LHgrid") ! 68% C.L.
! Print out values of mCharm and mBottom.
call GetQmassM(3,4,mCharm)
call GetQmassM(3,5,mBottom)
write(6,*) "mCharm,mBottom = ",mCharm,mBottom
! Print out values of alphaS(MZ) for each fit.
MZ = 91.1876D0
Call InitPDFM(1,0) ! central set
WRITE(6,'("LO: alphaS(MZ) = ",F7.5)') alphasPDF(MZ)
Call InitPDFM(2,0) ! central set
WRITE(6,'("NLO: alphaS(MZ) = ",F7.5)') alphasPDF(MZ)
Call InitPDFM(3,0) ! central set
WRITE(6,'("NNLO: alphaS(MZ) = ",F7.5)') alphasPDF(MZ)
! Warning: values of qcdl4 and qcdl5 set to zero since no longer used.
call GetLam4M(3,0,qcdl4)
call GetLam5M(3,0,qcdl5)
write(6,*) "qcdl4,qcdl5 = ",qcdl4,qcdl5
!----------------------------------------------------------------------
!-- Calculate the uncertainty on the parton distributions using both
!-- the formula for asymmetric errors [eqs.(51,52) of arXiv:0901.0002]
!-- and the formula for symmetric errors [eq.(50) of same paper].
!-- Select either the LO, NLO or NNLO fits.
! iset = 1 ! LO
! iset = 2 ! NLO
iset = 3 ! NNLO
!-- First get xf as a function of x at a fixed value of q.
!-- Extrapolation will be used for x < 10^-6.
q = 1.d1
nx = 100
xmin = 1.d-7
xmax = 0.99d0
DO flav = -5, 5
xfilename(flav) = "x"//flavours(flav)(1:len_trim(flavours(flav))) &
& //"_vs_x.dat"
OPEN(UNIT=20+flav,FILE=xfilename(flav))
WRITE(20+flav,'(" # q = ",1PE12.4)') q
WRITE(20+flav,'(A2,A10,4A12)') " #","x","x"// &
& flavours(flav)(1:len_trim(flavours(flav))), &
& "error+","error-","error"
END DO ! flav
DO ix = 1, nx
!-- Assign x values distributed logarithmically.
x = 10.d0**(log10(xmin) + (ix-1.D0)/(nx-1.D0)* &
& (log10(xmax)-log10(xmin)))
Call initPDFM(iset,0) ! central set
Call evolvePDFM(iset,x,q,xf)
DO flav = -5, 5
summax(flav) = 0.d0
summin(flav) = 0.d0
sum(flav) = 0.d0
END DO
Call numberPDFM(iset,nhess) ! number of eigenvector PDF sets
neigen = nhess/2
DO ieigen = 1, neigen ! loop over eigenvector sets
Call initPDFM(iset,2*ieigen-1) ! "+" direction
call evolvePDFM(iset,x,q,xfp)
Call initPDFM(iset,2*ieigen) ! "-" direction
call evolvePDFM(iset,x,q,xfm)
DO flav = -5, 5
summax(flav) = summax(flav) + &
& (max(xfp(flav)-xf(flav),xfm(flav)-xf(flav),0.d0))**2
summin(flav) = summin(flav) + &
& (max(xf(flav)-xfp(flav),xf(flav)-xfm(flav),0.d0))**2
sum(flav) = sum(flav)+(xfp(flav)-xfm(flav))**2
END DO ! flav
END DO ! ieigen
DO flav = -5, 5
WRITE(20+flav,'(1P5E12.4)') x,xf(flav), &
& sqrt(summax(flav)),sqrt(summin(flav)),0.5d0*sqrt(sum(flav))
END DO ! flav
END DO ! ix
DO flav = -5, 5
CLOSE(UNIT=20+flav)
WRITE(6,*) "x"//flavours(flav)(1:len_trim(flavours(flav))), &
& " vs. x for q2 = ",q**2," written to ", &
& xfilename(flav)(1:len_trim(xfilename(flav)))
END DO ! flav
!-- Now get xf as a function of q^2 at a fixed value of x.
!-- Extrapolation will be used for q^2 < 1 GeV^2 and for q^2 > 10^9 GeV^2.
x = 1.d-3
nq = 100
q2min = 5.d-1
q2max = 1.d10
DO flav = -5, 5
qfilename(flav) = "x"//flavours(flav)(1:len_trim(flavours(flav))) &
& //"_vs_q2.dat"
OPEN(UNIT=20+flav,FILE=qfilename(flav))
WRITE(20+flav,'(" # x = ",1PE12.4)') x
WRITE(20+flav,'(A2,A10,4A12)') " #","q2","x"// &
& flavours(flav)(1:len_trim(flavours(flav))), &
& "error+","error-","error"
END DO ! flav
DO iq = 1, nq
!-- Assign q2 values distributed logarithmically.
q = sqrt(10.d0**(log10(q2min) + (iq-1.D0)/(nq-1.D0)* &
& (log10(q2max)-log10(q2min))))
Call initPDFM(iset,0) ! central set
Call evolvePDFM(iset,x,q,xf)
DO flav = -5, 5
summax(flav) = 0.d0
summin(flav) = 0.d0
sum(flav) = 0.d0
END DO
Call numberPDFM(iset,nhess) ! number of eigenvector PDF sets
neigen = nhess/2
DO ieigen = 1, neigen ! loop over eigenvector sets
Call initPDFM(iset,2*ieigen-1) ! "+" direction
call evolvePDFM(iset,x,q,xfp)
Call initPDFM(iset,2*ieigen) ! "-" direction
call evolvePDFM(iset,x,q,xfm)
DO flav = -5, 5
summax(flav) = summax(flav) + &
& (max(xfp(flav)-xf(flav),xfm(flav)-xf(flav),0.d0))**2
summin(flav) = summin(flav) + &
& (max(xf(flav)-xfp(flav),xf(flav)-xfm(flav),0.d0))**2
sum(flav) = sum(flav)+(xfp(flav)-xfm(flav))**2
END DO ! flav
END DO ! ieigen
DO flav = -5, 5
WRITE(20+flav,'(1P5E12.4)') q**2,xf(flav), &
& sqrt(summax(flav)),sqrt(summin(flav)),0.5d0*sqrt(sum(flav))
END DO ! flav
END DO ! iq
DO flav = -5, 5
CLOSE(UNIT=20+flav)
WRITE(6,*) "x"//flavours(flav)(1:len_trim(flavours(flav))), &
& " vs. q2 for x = ",x," written to ", &
& qfilename(flav)(1:len_trim(qfilename(flav)))
END DO ! flav
STOP
END PROGRAM Example8
!----------------------------------------------------------------------
|
