TEvtGen/EvtGenModels/EvtLi2Spence.F

   1 C--------------------------------------------------------------------------
   2 C
   3 C Environment:
   4 C      This software is part of the EvtGen package developed jointly
   5 C      for the BaBar and CLEO collaborations.  If you use all or part
   6 C      of it, please give an appropriate acknowledgement.
   7 C
   8 C Copyright Information: See EvtGen/COPYRIGHT
   9 C      Copyright (C) 1998      Caltech, UCSB
  10 C
  11 C Module: EvtLi2Spence.F
  12 C
  13 C Description:
  14 C
  15 C Modification history:
  16 C
  17 C    DJL/RYD     August 11, 1998         Module created
  18 C
  19 C------------------------------------------------------------------------
  20 C -----------------------------------------------------------------
  21       DOUBLE PRECISION FUNCTION LI2SPENCE(X)
  22 C *************************************************************
  23 C REAL SPENCE FUNCTION OBTAINED FROM J. VAN DER BIJ
  24 C *************************************************************
  25        IMPLICIT REAL*8 (A-Z)
  26       COMPLEX*16 Y,Z,Z2,SP
  27       REAL*8 XR,XI,R2
  28       REAL*8 A1,A2,A3,A4,A5,A6,A7,A8,A9,A10,ZETA2
  29       DATA A1,A2,A3,A4,A5,A6,A7,A8,A9,A10,ZETA2/
  30      1 -0.250000000000000D0,
  31      2 -0.111111111111111D0,
  32      3 -0.010000000000000D0,
  33      4 -0.017006802721088D0,
  34      5 -0.019444444444444D0,
  35      6 -0.020661157024793D0,
  36      7 -0.021417300648069D0,
  37      8 -0.021948866377231D0,
  38      9 -0.022349233811171D0,
  39      1 -0.022663689135191D0,
  40      2  1.644934066848226D0/
  41
  42       LI2SPENCE=0
  43       XR=X
  44       XI=0.0D0
  45       R2=XR*XR+XI*XI
  46       IF(R2.GT.1.D0.AND.(XR/R2).GT.0.5D0)THEN
  47         Y=(X-1.D0)/X
  48         Z=-LOG(1.D0-Y)
  49         Z2=Z*Z
  50         SP=Z*(1.D0+A1*Z*(1.D0+A2*Z*(1.D0+A3*Z2*(1.D0+A4*Z2*
  51      1 (1.D0+A5*Z2*(1.D0+A6*Z2*(1.D0+A7*Z2*(1.D0+A8*Z2*(1.D0+A9*Z2*
  52      2 (1.D0+A10*Z2))))))))))
  53      3 +ZETA2-LOG(X)*LOG(1.D0-X)+0.5D0*LOG(X)**2
  54         LI=DREAL(SP)
  55         RETURN
  56             ELSEIF(R2.GT.1.D0.AND.(XR/R2).LE.0.5D0)THEN
  57         Y=1.D0/X
  58         Z=-LOG(1.D0-Y)
  59         Z2=Z*Z
  60         SP=-Z*(1.D0+A1*Z*(1.D0+A2*Z*(1.D0+A3*Z2*(1.D0+A4*Z2*
  61      1 (1.D0+A5*Z2*(1.D0+A6*Z2*(1.D0+A7*Z2*(1.D0+A8*Z2*(1.D0+A9*Z2*
  62      2 (1.D0+A10*Z2))))))))))
  63      3 -ZETA2-0.5D0*LOG(-X)**2
  64         LI=DREAL(SP)
  65         RETURN
  66       ELSEIF(R2.EQ.1.D0.AND.XI.EQ.0.D0)THEN
  67         SP=ZETA2
  68         LI=DREAL(SP)
  69         RETURN
  70       ELSEIF(R2.LE.1.D0.AND.XR.GT.0.5D0)THEN
  71         Y=1.D0-X
  72         Z=-LOG(1.D0-Y)
  73         Z2=Z*Z
  74         SP=-Z*(1.D0+A1*Z*(1.D0+A2*Z*(1.D0+A3*Z2*(1.D0+A4*Z2*
  75      1 (1.D0+A5*Z2*(1.D0+A6*Z2*(1.D0+A7*Z2*(1.D0+A8*Z2*(1.D0+A9*Z2*
  76      2 (1.D0+A10*Z2))))))))))
  77      3 +ZETA2-LOG(X)*LOG(1.D0-X)
  78        LI=DREAL(SP)
  79        RETURN
  80       ELSEIF(R2.LE.1.D0.AND.XR.LE.0.5D0)THEN
  81         Y=X
  82         Z=-LOG(1.D0-Y)
  83         Z2=Z*Z
  84         SP=Z*(1.D0+A1*Z*(1.D0+A2*Z*(1.D0+A3*Z2*(1.D0+A4*Z2*
  85      1 (1.D0+A5*Z2*(1.D0+A6*Z2*(1.D0+A7*Z2*(1.D0+A8*Z2*(1.D0+A9*Z2*
  86      2 (1.D0+A10*Z2))))))))))
  87         LI2SPENCE=DREAL(SP)
  88         RETURN
  89       ENDIF
  90       END
  91 C ----------------------------------------------------------------------
  92