hijing/src/pyhii3au.f

0001
0002 C***********************************************************************
0003
0004       FUNCTION PYHII3AU(BE,EPS,IREIM)
0005
0006 C...Calculates real and imaginary parts of the auxiliary function I3;
0007 C...see R. K. Ellis, I. Hinchliffe, M. Soldate and J. J. van der Bij,
0008 C...FERMILAB-Pub-87/100-T, LBL-23504, June, 1987
0009       COMMON/LUDAT1/MSTU(200),PARU(200),MSTJ(200),PARJ(200)
0010       SAVE /LUDAT1/
0011
0012       IF(EPS.LT.1.) GA=0.5*(1.+SQRT(1.-EPS))
0013
0014       IF(EPS.LT.0.) THEN
0015         F3RE=PYHISPEN((GA-1.)/(GA+BE-1.),0.,1)-
0016      &  PYHISPEN(GA/(GA+BE-1.),0.,1)+
0017      &  PYHISPEN((BE-GA)/BE,0.,1)-PYHISPEN((BE-GA)/(BE-1.),0.,1)+
0018      &  (LOG(BE)**2-LOG(BE-1.)**2)/2.+LOG(GA)*LOG((GA+BE-1.)/BE)+
0019      &  LOG(GA-1.)*LOG((BE-1.)/(GA+BE-1.))
0020         F3IM=0.
0021       ELSEIF(EPS.LT.1.) THEN
0022         F3RE=PYHISPEN((GA-1.)/(GA+BE-1.),0.,1)-
0023      &  PYHISPEN(GA/(GA+BE-1.),0.,1)+
0024      &  PYHISPEN(GA/(GA-BE),0.,1)-PYHISPEN((GA-1.)/(GA-BE),0.,1)+
0025      &  LOG(GA/(1.-GA))*LOG((GA+BE-1.)/(BE-GA))
0026         F3IM=-PARU(1)*LOG((GA+BE-1.)/(BE-GA))
0027       ELSE
0028         RSQ=EPS/(EPS-1.+(2.*BE-1.)**2)
0029         RCTHE=RSQ*(1.-2.*BE/EPS)
0030         RSTHE=SQRT(RSQ-RCTHE**2)
0031         RCPHI=RSQ*(1.+2.*(BE-1.)/EPS)
0032         RSPHI=SQRT(RSQ-RCPHI**2)
0033         R=SQRT(RSQ)
0034         THE=ACOS(RCTHE/R)
0035         PHI=ACOS(RCPHI/R)
0036         F3RE=PYHISPEN(RCTHE,RSTHE,1)+PYHISPEN(RCTHE,-RSTHE,1)-
0037      &  PYHISPEN(RCPHI,RSPHI,1)-PYHISPEN(RCPHI,-RSPHI,1)+
0038      &  (PHI-THE)*(PHI+THE-PARU(1))
0039         F3IM=PYHISPEN(RCTHE,RSTHE,2)+PYHISPEN(RCTHE,-RSTHE,2)-
0040      &  PYHISPEN(RCPHI,RSPHI,2)-PYHISPEN(RCPHI,-RSPHI,2)
0041       ENDIF
0042
0043       IF(IREIM.EQ.1) PYHII3AU=2./(2.*BE-1.)*F3RE
0044       IF(IREIM.EQ.2) PYHII3AU=2./(2.*BE-1.)*F3IM
0045
0046       RETURN
0047       END