GEANT321/ggeom/gnpara.F

   1 *
   2 * $Id$
   3 *
   4 * $Log$
   5 * Revision 1.1.1.1  1995/10/24 10:20:53  cernlib
   6 * Geant
   7 *
   8 *
   9 #include "geant321/pilot.h"
  10 *CMZ :  3.21/02 29/03/94  15.41.30  by  S.Giani
  11 *-- Author :
  12       SUBROUTINE GNPARA (X, PAR, IACT, SNEXT, SNXT, SAFE)
  13 C.
  14 C.    ******************************************************************
  15 C.    *                                                                *
  16 C.    *       COMPUTE DISTANCE UP TO INTERSECTION WITH 'PARA' VOLUME,  *
  17 C.    *       FROM INSIDE POINT X(1-3) ALONG DIRECTION X(4-6)          *
  18 C.    *                                                                *
  19 C.    *       PAR   (input)  : volume parameters                       *
  20 C.    *       IACT  (input)  : action flag                             *
  21 C.    *         = 0  Compute SAFE only                                 *
  22 C.    *         = 1  Compute SAFE, and SNXT only if SNEXT .GT.new SAFE *
  23 C.    *         = 2  Compute both SAFE and SNXT                        *
  24 C.    *         = 3  Compute SNXT only                                 *
  25 C.    *       SNEXT (input)  : see IACT = 1                            *
  26 C.    *       SNXT  (output) : distance to volume boundary             *
  27 C.    *       SAFE  (output) : shortest distance to any boundary       *
  28 C.    *                                                                *
  29 C.    *    ==>Called by : GNEXT, GTNEXT                                *
  30 C.    *         Author  A.McPherson  *********                         *
  31 C.    *                                                                *
  32 C.    ******************************************************************
  33 C.
  34 #include "geant321/gconsp.inc"
  35       DIMENSION X(6), PAR(6)
  36 C.
  37 C.    ---------------------------------------------------
  38 C.
  39       SNXT = BIG
  40       DN31=PAR(3)-X(3)
  41       DN32=-PAR(3)-X(3)
  42 C
  43       YT=X(2)-PAR(6)*X(3)
  44       DN21=PAR(2)-YT
  45       DN22=-PAR(2)-YT
  46       CTY=1.0/SQRT(1.0+PAR(6)**2)
  47 C
  48       XT=X(1)-PAR(5)*X(3)-PAR(4)*YT
  49       DN11=PAR(1)-XT
  50       DN12=-PAR(1)-XT
  51       CTX=1.0/SQRT(1.0+PAR(4)**2+PAR(5)**2)
  52
  53       IF (IACT .LT. 3) THEN
  54
  55
  56 C       -------------------------------------------------
  57 C       |  Compute safety-distance 'SAFE' (McPherson)   |
  58 C       -------------------------------------------------
  59
  60
  61         SAFE=MIN(DN11*CTX,-DN12*CTX,DN21*CTY,-DN22*CTY,DN31,-DN32)
  62 C
  63         IF (IACT .EQ. 0) GO TO 999
  64         IF (IACT .EQ. 1) THEN
  65           IF (SNEXT .LT. SAFE) GO TO 999
  66         ENDIF
  67       ENDIF
  68
  69 C     ------------------------------------------------
  70 C     |  Compute vector-distance 'SNXT' (McPherson)  |
  71 C     ------------------------------------------------
  72
  73
  74       SN3=BIG
  75       SN2=BIG
  76       SN1=BIG
  77 C
  78       IF(X(6).NE.0.0) SN3=DN31/X(6)
  79       IF(SN3.LT.0.0) SN3=DN32/X(6)
  80 C
  81       DY=X(5)-PAR(6)*X(6)
  82       IF(DY.NE.0.0) SN2=DN21/DY
  83       IF(SN2.LT.0.0) SN2=DN22/DY
  84 C
  85       DX=X(4)-PAR(5)*X(6)-PAR(4)*DY
  86       IF(DX.NE.0.0) SN1=DN11/DX
  87       IF(SN1.LT.0.0) SN1=DN12/DX
  88 C
  89       SNXT=MIN(SN1,SN2,SN3)
  90 C
  91   999 CONTINUE
  92       END