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*DECK PIJS3D
SUBROUTINE PIJS3D(NREG,NSOUT,NSLINE,WEIGHT,RCUTOF,SIGTAL,
> SEGLEN,NRSEG,STAYIN,GOSOUT,DPR)
*
*-----------------------------------------------------------------------
*
*Purpose:
* Integration for general 3D specular tracking.
*
*Copyright:
* Copyright (C) 1991 Ecole Polytechnique de Montreal
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version
*
*Author(s): R. Roy, G. Marleau
*
*Parameters: input
* NREG total number of regions.
* NSOUT number of outer surface.
* NSLINE number of segemnts on line.
* WEIGHT line weight.
* RCUTOF MFP cut-off factor (truncate lines).
* SIGTAL albedo-cross section vector.
* SEGLEN length of track.
* NRSEG region crossed by track.
*
*Parameters: output
* DPR collision probabilities.
*
*Parameters: scratch
* STAYIN stay-in zone probability.
* GOSOUT goes-out zone probability.
*
*References:
* R. Roy et al.,
* A Cyclic Tracking Procedure for CP Calculations in 2-D Lattices
* Conf/Advances in Math, Comp & Reactor Physics,
* Pittsburgh, V 1, P 2.2 4-1 (1991).
*
*-----------------------------------------------------------------------
*
IMPLICIT NONE
*----
* VARIABLES
*----
INTEGER NREG,NSOUT,NSLINE,NRSEG(NSLINE)
REAL RCUTOF,SIGTAL(-NSOUT:NREG)
DOUBLE PRECISION WEIGHT,SEGLEN(NSLINE),STAYIN(NSLINE),
> GOSOUT(NSLINE)
DOUBLE PRECISION DPR(-NSOUT:NREG,-NSOUT:NREG)
*----
* Local variables
*----
INTEGER IL,JL,NOIL,NOJL,ISODD,JSODD,IJDEL
DOUBLE PRECISION TTOT,XSIL,OPATH,FINV,CUTOF
REAL ZERO,ONE,HALF
PARAMETER (ZERO=0.0E0, ONE=1.0E0, HALF=0.5E0 )
REAL SIXT,CUTEXP
PARAMETER (SIXT=HALF/3.0,CUTEXP=0.02)
DOUBLE PRECISION EXSIL,XSIL2
TTOT= ONE
*
*1.1) CHANGE PATHS => GOSOUT AND STAYIN PATHS, INCLUDING ALBEDOS
* ADD *PII* LOCAL NON-CYCLIC CONTRIBUTIONS
ISODD=0
DO 30 IL= 1, NSLINE
NOIL = NRSEG(IL)
IF( NOIL.LT.0 )THEN
IF(ISODD .EQ. 1) THEN
ISODD=0
*----
* FOR SURFACES:
* OLD VERSION BEFORE SURFACE DOUBLING
* GOSOUT= ALBEDO * SURFACE WEIGHT
* WHERE ALL SURFACE WEIGHTS WERE 1.0
* NEW VERSION WITH SURFACE DOUBLING
* GOSOUT= ALBEDO
* STAYIN = 1- ALBEDO * SURFACE WEIGHT
* TTOT = PRODUCT OF GOSOUT
*----
GOSOUT(IL)= SIGTAL(NOIL)
STAYIN(IL)= ONE - GOSOUT(IL)
TTOT= TTOT * GOSOUT(IL)
ELSE
ISODD=1
*----
* FOR SURFACES:
* OLD VERSION BEFORE SURFACE DOUBLING
* GOSOUT= ALBEDO * SURFACE WEIGHT
* WHERE ALL SURFACE WEIGHTS WERE 1.0
* NEW VERSION WITH SURFACE DOUBLING
* GOSOUT= ALBEDO
* STAYIN = 1- ALBEDO * SURFACE WEIGHT
* TTOT = PRODUCT OF GOSOUT
*----
GOSOUT(IL)= SIGTAL(NOIL)
STAYIN(IL)= ONE
ENDIF
ELSE
*----
* FOR REGIONS
* STAYIN = 1 - EXP[ -CROSS SECTION * LENGTH OF NSLINE]
* GOSOUT = 1 - STAYIN
* TTOT = PRODUCT OF GOSOUT
*----
XSIL = SIGTAL(NOIL)
IF( XSIL .EQ. ZERO) THEN
GOSOUT(IL)= ONE
STAYIN(IL)= SEGLEN(IL)
DPR(NOIL,NOIL)= DPR(NOIL,NOIL)
> + HALF*WEIGHT*STAYIN(IL)*STAYIN(IL)
ELSE IF( XSIL .LT. CUTEXP) THEN
OPATH= SIGTAL(NOIL)*SEGLEN(IL)
XSIL2=OPATH*OPATH
EXSIL=XSIL2*(HALF-SIXT*OPATH+XSIL2/24.0)
STAYIN(IL)=OPATH-EXSIL
GOSOUT(IL)= ONE - STAYIN(IL)
TTOT= TTOT * GOSOUT(IL)
DPR(NOIL,NOIL)= DPR(NOIL,NOIL) + WEIGHT*EXSIL
ELSE
OPATH= SIGTAL(NOIL)*SEGLEN(IL)
EXSIL= EXP(-OPATH)
STAYIN(IL)= ONE - EXSIL
GOSOUT(IL)= EXSIL
TTOT= TTOT * GOSOUT(IL)
DPR(NOIL,NOIL)= DPR(NOIL,NOIL)
> + WEIGHT*(OPATH-STAYIN(IL))
ENDIF
ENDIF
30 CONTINUE
*
*1.2) COMPUTE CYCLIC FACTORS BY ANGLE
* USING GLOBAL TRACK ATTENUATION: BETA(TOT)*EXP(-MFP(TOT))
IF(TTOT .GE. ONE )THEN
CALL XABORT( 'PIJS3D: ALBEDOS ARE NOT COMPATIBLE')
ENDIF
FINV= WEIGHT / (ONE-TTOT)
*
*1.3) ADD *PIJ* CONTRIBUTIONS FOR FORWARD SOURCES
ISODD=0
DO 50 IL= 1, NSLINE
NOIL = NRSEG(IL)
TTOT= FINV * STAYIN(IL)
CUTOF= RCUTOF*TTOT
IF( NOIL .LT. 0) THEN
ISODD=MOD(ISODD+1,2)
JSODD=ISODD
DO 70 IJDEL= 1, NSLINE
JL= MOD(IL+IJDEL-1,NSLINE) + 1
NOJL=NRSEG(JL)
IF( NOJL .LT. 0 ) THEN
JSODD=MOD(JSODD+1,2)
IF( ISODD.EQ.1 .AND. JSODD .EQ.0) THEN
DPR(NOJL,NOIL)= DPR(NOJL,NOIL) + TTOT * STAYIN(JL)
TTOT= TTOT * GOSOUT(JL)
IF( TTOT.LE.CUTOF ) GO TO 55
ENDIF
ELSE IF(ISODD.EQ.1) THEN
DPR(NOJL,NOIL)= DPR(NOJL,NOIL) + TTOT * STAYIN(JL)
TTOT= TTOT * GOSOUT(JL)
IF( TTOT.LE.CUTOF ) GO TO 55
ENDIF
70 CONTINUE
ELSE
JSODD=ISODD
DO 80 IJDEL= 1, NSLINE
JL= MOD(IL+IJDEL-1,NSLINE) + 1
NOJL=NRSEG(JL)
IF( NOJL .LT. 0 ) THEN
JSODD=MOD(JSODD+1,2)
IF( JSODD .EQ.0) THEN
DPR(NOJL,NOIL)= DPR(NOJL,NOIL) + TTOT * STAYIN(JL)
TTOT= TTOT * GOSOUT(JL)
IF( TTOT.LE.CUTOF ) GO TO 55
ENDIF
ELSE
DPR(NOJL,NOIL)= DPR(NOJL,NOIL) + TTOT * STAYIN(JL)
TTOT= TTOT * GOSOUT(JL)
IF( TTOT.LE.CUTOF ) GO TO 55
ENDIF
80 CONTINUE
ENDIF
55 CONTINUE
50 CONTINUE
RETURN
END
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