[u/mrichter/AliRoot.git] / HERWIG / src / hwhew2.f


CDECK  ID>, HWHEW2.

*CMZ :-        -26/04/91  13.22.25  by  Federico Carminati

*-- Author :    Zoltan Kunszt, modified by Bryan Webber

C-----------------------------------------------------------------------

      SUBROUTINE HWHEW2(NPART,PPCM,H,CH,D)

C-----------------------------------------------------------------------

C PCM SHOULD BE DEFINED SUCH THAT ALL 4-MOMENTA ARE OUTGOING.

C CONVENTION FOR PCM AND P IS THAT DIRECTION 1 =BEAM, COMPONENT

C 4 = ENERGY AND COMPONENT 2 AND 3 ARE TRANSVERSE COMPONENTS.

C THUS INCOMING MOMENTA SHOULD CORRESPOND TO OUTGOING MOMENTA

C OF NEGATIVE ENERGY.

C PCM IS FILLED BY PHASE SPACE MONTE CARLO.

C I1-I7 HERE REFER TO HOW PCM INDEXING IS MAPPED TO OUR STANDARD

C 1-6=GLUON,GLUON,Q,QBAR,QP,QPBAR ORDERING `

C-----------------------------------------------------------------------

      IMPLICIT NONE

      COMPLEX PT5,ZT,Z1,ZI,ZP,ZQ,ZD,ZPS,ZQS,ZDPM,ZDMP,H(7,7),CH(7,7),

     & D(7,7)

      DOUBLE PRECISION ZERO,ONE,PPCM(5,7),P(5,7),WRN(7),EPS,Q1,Q2,QP,QM,

     & P1,P2,PP,PM,DMP,DPM,PT,QT,PTI,QTI

      INTEGER J,L,IJ,II,JJ,I,NPART,IP1,IPP1

      PARAMETER (ZERO=0.D0,ONE=1.D0)

      EPS=0.0000001

      ZI=CMPLX(0.,1.)

      Z1=CMPLX(1.,0.)

C FOLLOWING DO LOOP IS TO CONVERT TO OUR STANDARD INDEXING

      DO 1 L=1,NPART

      DO 1 IJ=1,4

1     P(IJ,L)=PPCM(IJ,L)

      DO 2 II=1,7

      WRN(II)=ONE

      IF(P(4,II).LT.ZERO) WRN(II)=-ONE

      DO 2 JJ=1,4

      P(JJ,II)=WRN(II)*P(JJ,II)

    2 CONTINUE

C THE ABOVE CHECKS FOR MOMENTA WITH NEGATIVE ENERGY,INNER PRODUCTS

C ARE EXPRESSED DIFFERENTLY FOR DIFFERENT CASES

      DO 11 I=1,NPART-1

      IP1=I+1

      DO 11 J=IP1,NPART

      Q1=P(4,I)+P(1,I)

      QP=0.0

      IF(Q1.GT.EPS)QP=SQRT(Q1)

      Q2=P(4,I)-P(1,I)

      QM=0.0

      IF(Q2.GT.EPS)QM=SQRT(Q2)

      P1=P(4,J)+P(1,J)

      PP=0.

      IF(P1.GT.EPS)PP=SQRT(P1)

      P2=P(4,J)-P(1,J)

      PM=0.

      IF(P2.GT.EPS)PM=SQRT(P2)

      DMP=PM*QP

      ZDMP=CMPLX(DMP,ZERO)

      DPM=PP*QM

      ZDPM=CMPLX(DPM,ZERO)

C NOTE THAT IN OUR INNER PRODUCT NOTATION WE ARE COMPUTING <P,Q>

      PT=SQRT(P(2,J)**2+P(3,J)**2)

      QT=SQRT(P(2,I)**2+P(3,I)**2)

      IF(PT.GT.EPS) GOTO 99

      ZP=Z1

      GOTO 98

   99 PTI=ONE/PT

      ZP=CMPLX(PTI*P(2,J),PTI*P(3,J))

   98 ZPS=CONJG(ZP)

      IF(QT.GT.EPS) GOTO 89

      ZQ=Z1

      GOTO 88

   89 QTI=ONE/QT

      ZQ=CMPLX(QTI*P(2,I),QTI*P(3,I))

   88 ZQS=CONJG(ZQ)

      ZT=Z1

      IF(WRN(I).LT.ZERO) ZT=ZT*ZI

      IF(WRN(J).LT.ZERO) ZT=ZT*ZI

      H(J,I)=(ZDMP*ZP-ZDPM*ZQ)*ZT

      CH(J,I)=(ZDMP*ZPS-ZDPM*ZQS)*ZT

      ZD=H(J,I)*CH(J,I)

      PT5=CMPLX(.5,0.)

      D(J,I)=PT5*ZD

   11 CONTINUE

      DO 60 I=1,NPART-1

      IPP1=I+1

      DO 60 J=IPP1,NPART

      H(I,J)=-H(J,I)

      CH(I,J)=-CH(J,I)

   60 D(I,J)=D(J,I)

      RETURN

      END
Commit	Line	Data
3820ca8e	1
	2	CDECK ID>, HWHEW2.
	3
	4	*CMZ :- -26/04/91 13.22.25 by Federico Carminati
	5
	6	*-- Author : Zoltan Kunszt, modified by Bryan Webber
	7
	8	C-----------------------------------------------------------------------
	9
	10	SUBROUTINE HWHEW2(NPART,PPCM,H,CH,D)
	11
	12	C-----------------------------------------------------------------------
	13
	14	C PCM SHOULD BE DEFINED SUCH THAT ALL 4-MOMENTA ARE OUTGOING.
	15
	16	C CONVENTION FOR PCM AND P IS THAT DIRECTION 1 =BEAM, COMPONENT
	17
	18	C 4 = ENERGY AND COMPONENT 2 AND 3 ARE TRANSVERSE COMPONENTS.
	19
	20	C THUS INCOMING MOMENTA SHOULD CORRESPOND TO OUTGOING MOMENTA
	21
	22	C OF NEGATIVE ENERGY.
	23
	24	C PCM IS FILLED BY PHASE SPACE MONTE CARLO.
	25
	26	C I1-I7 HERE REFER TO HOW PCM INDEXING IS MAPPED TO OUR STANDARD
	27
	28	C 1-6=GLUON,GLUON,Q,QBAR,QP,QPBAR ORDERING `
	29
	30	C-----------------------------------------------------------------------
	31
	32	IMPLICIT NONE
	33
	34	COMPLEX PT5,ZT,Z1,ZI,ZP,ZQ,ZD,ZPS,ZQS,ZDPM,ZDMP,H(7,7),CH(7,7),
	35
	36	& D(7,7)
	37
	38	DOUBLE PRECISION ZERO,ONE,PPCM(5,7),P(5,7),WRN(7),EPS,Q1,Q2,QP,QM,
	39
	40	& P1,P2,PP,PM,DMP,DPM,PT,QT,PTI,QTI
	41
	42	INTEGER J,L,IJ,II,JJ,I,NPART,IP1,IPP1
	43
	44	PARAMETER (ZERO=0.D0,ONE=1.D0)
	45
	46	EPS=0.0000001
	47
	48	ZI=CMPLX(0.,1.)
	49
	50	Z1=CMPLX(1.,0.)
	51
	52	C FOLLOWING DO LOOP IS TO CONVERT TO OUR STANDARD INDEXING
	53
	54	DO 1 L=1,NPART
	55
	56	DO 1 IJ=1,4
	57
	58	1 P(IJ,L)=PPCM(IJ,L)
	59
	60	DO 2 II=1,7
	61
	62	WRN(II)=ONE
	63
	64	IF(P(4,II).LT.ZERO) WRN(II)=-ONE
65
66	DO 2 JJ=1,4
67
68	P(JJ,II)=WRN(II)*P(JJ,II)
69
70	2 CONTINUE
71
72	C THE ABOVE CHECKS FOR MOMENTA WITH NEGATIVE ENERGY,INNER PRODUCTS
73
74	C ARE EXPRESSED DIFFERENTLY FOR DIFFERENT CASES
75
76	DO 11 I=1,NPART-1
77
78	IP1=I+1
79
80	DO 11 J=IP1,NPART
81
82	Q1=P(4,I)+P(1,I)
83
84	QP=0.0
85
86	IF(Q1.GT.EPS)QP=SQRT(Q1)
87
88	Q2=P(4,I)-P(1,I)
89
90	QM=0.0
91
92	IF(Q2.GT.EPS)QM=SQRT(Q2)
93
94	P1=P(4,J)+P(1,J)
95
96	PP=0.
97
98	IF(P1.GT.EPS)PP=SQRT(P1)
99
100	P2=P(4,J)-P(1,J)
101
102	PM=0.
103
104	IF(P2.GT.EPS)PM=SQRT(P2)
105
106	DMP=PM*QP
107
108	ZDMP=CMPLX(DMP,ZERO)
109
110	DPM=PP*QM
111
112	ZDPM=CMPLX(DPM,ZERO)
113
114	C NOTE THAT IN OUR INNER PRODUCT NOTATION WE ARE COMPUTING <P,Q>
115
116	PT=SQRT(P(2,J)2+P(3,J)2)
117
118	QT=SQRT(P(2,I)2+P(3,I)2)
119
120	IF(PT.GT.EPS) GOTO 99
121
122	ZP=Z1
123
124	GOTO 98
125
126	99 PTI=ONE/PT
127
128	ZP=CMPLX(PTIP(2,J),PTIP(3,J))
129
130	98 ZPS=CONJG(ZP)
131
132	IF(QT.GT.EPS) GOTO 89
133
134	ZQ=Z1
135
136	GOTO 88
137
138	89 QTI=ONE/QT
139
140	ZQ=CMPLX(QTIP(2,I),QTIP(3,I))
141
142	88 ZQS=CONJG(ZQ)
143
144	ZT=Z1
145
146	IF(WRN(I).LT.ZERO) ZT=ZT*ZI
147
148	IF(WRN(J).LT.ZERO) ZT=ZT*ZI
149
150	H(J,I)=(ZDMPZP-ZDPMZQ)*ZT
151
152	CH(J,I)=(ZDMPZPS-ZDPMZQS)*ZT
153
154	ZD=H(J,I)*CH(J,I)
155
156	PT5=CMPLX(.5,0.)
157
158	D(J,I)=PT5*ZD
159
160	11 CONTINUE
161
162	DO 60 I=1,NPART-1
163
164	IPP1=I+1
165
166	DO 60 J=IPP1,NPART
167
168	H(I,J)=-H(J,I)
169
170	CH(I,J)=-CH(J,I)
171
172	60 D(I,J)=D(J,I)
173
174	RETURN
175
176	END