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partonx5.F
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1 
2  FUNCTION partonx5 (IPRTN, X, Q)
3 C
4 C Given the parton distribution function in the array Upd in
5 C COMMON / CtqPar1 / , this routine fetches u(fl, x, q) at any value of
6 C x and q using Mth-order polynomial interpolation for x and Ln(Q/Lambda).
7 C
8  IMPLICIT DOUBLE PRECISION (a-h, o-z)
9 C
10  parameter(mxx = 105, mxq = 25, mxf = 6)
11  parameter(mxpqx = (mxf *2 +2) * mxq * mxx)
12  parameter(m= 2, m1 = m + 1)
13 C
14  Logical first
15  Common
16  > / ctqpar1 / al, xv(0:mxx), ql(0:mxq), upd(mxpqx)
17  > / ctqpar2 / nx, nt, nfmx
18  > / xqrange / qini, qmax, xmin
19 C
20  dimension fq(m1), df(m1)
21 
22  Data first /.true./
23  save first
24 C Work with Log (Q)
25  qg = log(q/al)
26 
27 C Find lower end of interval containing X
28  jl = -1
29  ju = nx+1
30  11 If (ju-jl .GT. 1) Then
31  jm = (ju+jl) / 2
32  If (x .GT. xv(jm)) Then
33  jl = jm
34  Else
35  ju = jm
36  Endif
37  goto 11
38  Endif
39 
40  jx = jl - (m-1)/2
41  If (x .lt. xmin .and. first ) Then
42  first = .false.
43  print '(A, 2(1pE12.4))',
44  > ' WARNING: X << Xmin, extrapolation used; X, Xmin =', x, xmin
45  If (jx .LT. 0) jx = 0
46  Elseif (jx .GT. nx-m) Then
47  jx = nx - m
48  Endif
49 C Find the interval where Q lies
50  jl = -1
51  ju = nt+1
52  12 If (ju-jl .GT. 1) Then
53  jm = (ju+jl) / 2
54  If (qg .GT. ql(jm)) Then
55  jl = jm
56  Else
57  ju = jm
58  Endif
59  goto 12
60  Endif
61 
62  jq = jl - (m-1)/2
63  If (jq .LT. 0) Then
64  jq = 0
65  If (q .lt. qini) print '(A, 2(1pE12.4))',
66  > ' WARNING: Q << Qini, extrapolation used; Q, Qini =', q, qini
67  Elseif (jq .GT. nt-m) Then
68  jq = nt - m
69  If (q .gt. qmax) print '(A, 2(1pE12.4))',
70  > ' WARNING: Q > Qmax, extrapolation used; Q, Qmax =', q, qmax
71  Endif
72 
73  If (iprtn .GE. 3) Then
74  ip = - iprtn
75  Else
76  ip = iprtn
77  EndIf
78 C Find the off-set in the linear array Upd
79  jfl = ip + nfmx
80  j0 = (jfl * (nt+1) + jq) * (nx+1) + jx
81 C
82 C Now interpolate in x for M1 Q's
83  Do 21 iq = 1, m1
84  j1 = j0 + (nx+1)*(iq-1) + 1
85  Call polint5(xv(jx), upd(j1), m1, x, fq(iq), df(iq))
86  21 Continue
87 C Finish off by interpolating in Q
88  Call polint5(ql(jq), fq(1), m1, qg, ftmp, ddf)
89 
90  partonx5 = ftmp
91 C
92  RETURN
93 C ****************************
94  END