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Commit | Line | Data |
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fe4da5cc | 1 | |
2 | C*********************************************************************** | |
3 | ||
4 | FUNCTION PYSPEN(XREIN,XIMIN,IREIM) | |
5 | ||
6 | C...Calculates real and imaginary part of Spence function; see | |
7 | C...G. 't Hooft and M. Veltman, Nucl. Phys. B153 (1979) 365. | |
8 | COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200) | |
9 | SAVE /LUDAT1/ | |
10 | DIMENSION B(0:14) | |
11 | ||
12 | DATA B/ | |
13 | & 1.000000E+00, -5.000000E-01, 1.666667E-01, | |
14 | & 0.000000E+00, -3.333333E-02, 0.000000E+00, | |
15 | & 2.380952E-02, 0.000000E+00, -3.333333E-02, | |
16 | & 0.000000E+00, 7.575757E-02, 0.000000E+00, | |
17 | &-2.531135E-01, 0.000000E+00, 1.166667E+00/ | |
18 | ||
19 | XRE=XREIN | |
20 | XIM=XIMIN | |
21 | IF(ABS(1.-XRE).LT.1.E-6.AND.ABS(XIM).LT.1.E-6) THEN | |
22 | IF(IREIM.EQ.1) PYSPEN=PARU(1)**2/6. | |
23 | IF(IREIM.EQ.2) PYSPEN=0. | |
24 | RETURN | |
25 | ENDIF | |
26 | ||
27 | XMOD=SQRT(XRE**2+XIM**2) | |
28 | IF(XMOD.LT.1.E-6) THEN | |
29 | IF(IREIM.EQ.1) PYSPEN=0. | |
30 | IF(IREIM.EQ.2) PYSPEN=0. | |
31 | RETURN | |
32 | ENDIF | |
33 | ||
34 | XARG=SIGN(ACOS(XRE/XMOD),XIM) | |
35 | SP0RE=0. | |
36 | SP0IM=0. | |
37 | SGN=1. | |
38 | IF(XMOD.GT.1.) THEN | |
39 | ALGXRE=LOG(XMOD) | |
40 | ALGXIM=XARG-SIGN(PARU(1),XARG) | |
41 | SP0RE=-PARU(1)**2/6.-(ALGXRE**2-ALGXIM**2)/2. | |
42 | SP0IM=-ALGXRE*ALGXIM | |
43 | SGN=-1. | |
44 | XMOD=1./XMOD | |
45 | XARG=-XARG | |
46 | XRE=XMOD*COS(XARG) | |
47 | XIM=XMOD*SIN(XARG) | |
48 | ENDIF | |
49 | IF(XRE.GT.0.5) THEN | |
50 | ALGXRE=LOG(XMOD) | |
51 | ALGXIM=XARG | |
52 | XRE=1.-XRE | |
53 | XIM=-XIM | |
54 | XMOD=SQRT(XRE**2+XIM**2) | |
55 | XARG=SIGN(ACOS(XRE/XMOD),XIM) | |
56 | ALGYRE=LOG(XMOD) | |
57 | ALGYIM=XARG | |
58 | SP0RE=SP0RE+SGN*(PARU(1)**2/6.-(ALGXRE*ALGYRE-ALGXIM*ALGYIM)) | |
59 | SP0IM=SP0IM-SGN*(ALGXRE*ALGYIM+ALGXIM*ALGYRE) | |
60 | SGN=-SGN | |
61 | ENDIF | |
62 | ||
63 | XRE=1.-XRE | |
64 | XIM=-XIM | |
65 | XMOD=SQRT(XRE**2+XIM**2) | |
66 | XARG=SIGN(ACOS(XRE/XMOD),XIM) | |
67 | ZRE=-LOG(XMOD) | |
68 | ZIM=-XARG | |
69 | ||
70 | SPRE=0. | |
71 | SPIM=0. | |
72 | SAVERE=1. | |
73 | SAVEIM=0. | |
74 | DO 100 I=0,14 | |
75 | IF(MAX(ABS(SAVERE),ABS(SAVEIM)).LT.1E-30) GOTO 110 | |
76 | TERMRE=(SAVERE*ZRE-SAVEIM*ZIM)/FLOAT(I+1) | |
77 | TERMIM=(SAVERE*ZIM+SAVEIM*ZRE)/FLOAT(I+1) | |
78 | SAVERE=TERMRE | |
79 | SAVEIM=TERMIM | |
80 | SPRE=SPRE+B(I)*TERMRE | |
81 | SPIM=SPIM+B(I)*TERMIM | |
82 | 100 CONTINUE | |
83 | ||
84 | 110 IF(IREIM.EQ.1) PYSPEN=SP0RE+SGN*SPRE | |
85 | IF(IREIM.EQ.2) PYSPEN=SP0IM+SGN*SPIM | |
86 | ||
87 | RETURN | |
88 | END |