[u/mrichter/AliRoot.git] / GEANT321 / neutron / cangle.F

*
* $Id$
*
* $Log$
* Revision 1.1.1.1  1995/10/24 10:21:55  cernlib
* Geant
*
*
#include "geant321/pilot.h"
*CMZ :  3.21/04 23/02/95  14.46.01  by  S.Giani
*-- Author :
      SUBROUTINE CANGLE(D,LD,E,FM,LEN)
C       THIS ROUTINE SELECTS THE SCATTERING ANGLE AT A COLLISION
      DIMENSION D(*),LD(*)
      SAVE
      I=0
      IPP=1
      NR=LD(IPP)
      NE=LD(IPP+1)
      NR2=2*NR
      IP=2+NR2
      INT=LD(IP)
   10 IP=IP+1
      I=I+1
      EINCD=D(IP)
      IF(E.LE.EINCD)GO TO 30
      IP1=IP
      IP=IP+1
      NP=LD(IP)
      IP=IP+2*NP
      IF(IP.GE.LEN)GO TO 20
      GO TO 10
C       E IS GREATER THAN THE LAST INCIDENT ENERGY
C       USE THE LAST DISTRIBUTION
   20 IP=IP-2*NP-1
      GO TO 70
   30 IF(I.EQ.1)GO TO 60
C       CHOOSE WHICH DISTRIBUTION TO SAMPLE FROM
C       THE INTERPOLATION SCHEME IS ASSUMED LINEAR-LINEAR IF IT
C       IS NOT EQUAL TO THREE (LINEAR-LOG).  THIS IS GENERALLY TRUE
      IF(INT.NE.3)GO TO 40
      PROB=ALOG(EINCD/E)/ALOG(EINCD/D(IP1))
   40 PROB=(EINCD-E)/(EINCD-D(IP1))
      R=FLTRNF(0)
      IF(R.LE.PROB)GO TO 50
C       SELECT FROM THE SECOND DISTRIBUTION
      NP=LD(IP+1)
      GO TO 70
C       SELECT FROM THE FIRST DISTRIBUTION
   50 IP=IP1
      GO TO 70
C       E IS LESS THAN THE FIRST INCIDENT ENERGY
C       USE THE FIRST DISTRIBUTION
   60 NP=LD(IP+1)
   70 CONTINUE
      PROB1=0.0
      R=FLTRNF(0)
      DO 80 I=2,NP
         N=IP+2*I+1
         A1=D(N-3)
         IF(R.LE.D(N))GO TO 90
         PROB1=D(N)
   80 CONTINUE
      FM=1.0
      RETURN
   90 FM=A1+(R-PROB1)*(D(N-1)-A1)/(D(N)-PROB1)
      IF(ABS(FM).GT.1.) FM = 1.0
      RETURN
      END
Commit	Line	Data
fe4da5cc	1	*
	2	* $Id$
	3	*
	4	* $Log$
	5	* Revision 1.1.1.1 1995/10/24 10:21:55 cernlib
	6	* Geant
	7	*
	8	*
	9	#include "geant321/pilot.h"
	10	*CMZ : 3.21/04 23/02/95 14.46.01 by S.Giani
	11	*-- Author :
	12	SUBROUTINE CANGLE(D,LD,E,FM,LEN)
	13	C THIS ROUTINE SELECTS THE SCATTERING ANGLE AT A COLLISION
	14	DIMENSION D(),LD()
	15	SAVE
	16	I=0
	17	IPP=1
	18	NR=LD(IPP)
	19	NE=LD(IPP+1)
	20	NR2=2*NR
	21	IP=2+NR2
	22	INT=LD(IP)
	23	10 IP=IP+1
	24	I=I+1
	25	EINCD=D(IP)
	26	IF(E.LE.EINCD)GO TO 30
	27	IP1=IP
	28	IP=IP+1
	29	NP=LD(IP)
	30	IP=IP+2*NP
	31	IF(IP.GE.LEN)GO TO 20
	32	GO TO 10
	33	C E IS GREATER THAN THE LAST INCIDENT ENERGY
	34	C USE THE LAST DISTRIBUTION
	35	20 IP=IP-2*NP-1
	36	GO TO 70
	37	30 IF(I.EQ.1)GO TO 60
	38	C CHOOSE WHICH DISTRIBUTION TO SAMPLE FROM
	39	C THE INTERPOLATION SCHEME IS ASSUMED LINEAR-LINEAR IF IT
	40	C IS NOT EQUAL TO THREE (LINEAR-LOG). THIS IS GENERALLY TRUE
	41	IF(INT.NE.3)GO TO 40
	42	PROB=ALOG(EINCD/E)/ALOG(EINCD/D(IP1))
	43	40 PROB=(EINCD-E)/(EINCD-D(IP1))
	44	R=FLTRNF(0)
	45	IF(R.LE.PROB)GO TO 50
	46	C SELECT FROM THE SECOND DISTRIBUTION
	47	NP=LD(IP+1)
	48	GO TO 70
	49	C SELECT FROM THE FIRST DISTRIBUTION
	50	50 IP=IP1
	51	GO TO 70
	52	C E IS LESS THAN THE FIRST INCIDENT ENERGY
	53	C USE THE FIRST DISTRIBUTION
	54	60 NP=LD(IP+1)
	55	70 CONTINUE
	56	PROB1=0.0
	57	R=FLTRNF(0)
	58	DO 80 I=2,NP
	59	N=IP+2*I+1
	60	A1=D(N-3)
	61	IF(R.LE.D(N))GO TO 90
	62	PROB1=D(N)
	63	80 CONTINUE
	64	FM=1.0
65	RETURN
66	90 FM=A1+(R-PROB1)*(D(N-1)-A1)/(D(N)-PROB1)
67	IF(ABS(FM).GT.1.) FM = 1.0
68	RETURN
69	END