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1 *
2 * $Id$
3 *
4 * $Log$
5 * Revision 1.1.1.1  1995/10/24 10:20:52  cernlib
6 * Geant
7 *
8 *
9 #include "geant321/pilot.h"
10 *CMZ :  3.21/02 29/03/94  15.41.29  by  S.Giani
11 *-- Author :
12       SUBROUTINE GNHYPE (X, PAR, IACT, SNEXT, SNXT, SAFE)
13 C.
14 C.    ******************************************************************
15 C.    *                                                                *
16 C.    *      COMPUTE DISTANCE UP TO INTERSECTION WITH  HYPErboloid     *
17 C.    *      VOLUME FROM INSIDE POINT X(1-3) ALONG DIRECTION X(4-6)    *
18 C.    *                                                                *
19 C.    *       PAR   (input)  : volume parameters                       *
20 C.    *                        inner radius                            *
21 C.    *                        outer radius                            *
22 C.    *                        half length in z                        *
23 C.    *                        straw stereo angle in degrees           *
24 C.    *                        r**2 = (z*tan(theta))**2 + a**2         *
25 C.    *                                                                *
26 C.    *       IACT  (input)  : action flag                             *
27 C.    *         = 0  Compute SAFE only                                 *
28 C.    *         = 1  Compute SAFE, and SNXT only if SNEXT .GT.new SAFE *
29 C.    *         = 2  Compute both SAFE and SNXT                        *
30 C.    *         = 3  Compute SNXT only                                 *
31 C.    *       SNEXT (input)  : see IACT = 1                            *
32 C.    *       SNXT  (output) : distance to volume boundary             *
33 C.    *       SAFE  (output) : shortest distance to any boundary       *
34 C.    *                                                                *
35 C.    *    ==>Called by : GNEXT, GTNEXT                                *
36 C.    *         Authors M.J. Corden,  A.Palounek                       *
37 C.    *                                                                *
38 C.    ******************************************************************
39 C.
40 #include "geant321/gconsp.inc"
41       DIMENSION X(6),PAR(4)
42  
43 C-------------------------------------------------------------
44  
45       SNXT = BIG
46       R2   = X(1)*X(1) + X(2)*X(2)
47       TANTHS=(TAN(PAR(4)*DEGRAD))**2
48  
49 C       -------------------------------------------------
50 C       |  Compute safety-distance 'SAFE' (P.Weidhaas)  |
51 C       -------------------------------------------------
52  
53       SAFZ1  = PAR(3) - X(3)
54       SAFZ2  = PAR(3) + X(3)
55  
56       IF (IACT .LT. 3) THEN
57  
58 C    tube version:
59 C      R    = SQRT (R2)
60 C      IF (PAR(1).NE.0.) THEN
61 C         SAFR1  = R - PAR(1)
62 C      ELSE
63 C         SAFR1  = BIG
64 C      ENDIF
65 C      SAFR2  = PAR(2) - R
66 C
67 C        SAFE  = MIN (SAFZ1, SAFZ2, SAFR1, SAFR2)
68 C
69 C    simple, safe choice for hyperboloid for now:
70       SAFE=0.
71 C
72         IF (IACT .EQ. 0) GO TO 999
73         IF (IACT .EQ. 1) THEN
74           IF (SNEXT .LT. SAFE) GO TO 999
75         ENDIF
76       ENDIF
77  
78 C     ------------------------------------------------
79 C     |  Compute vector-distance 'SNXT' (McPherson)  |
80 C     ------------------------------------------------
81  
82 C
83 C             Compute intersection with z-boundaries.
84 C
85       IF(X(6).GT.0.)THEN
86          SNXT=SAFZ1/X(6)
87       ELSEIF(X(6).LT.0.)THEN
88          SNXT=-SAFZ2/X(6)
89       ENDIF
90 C
91 C     Compute intercepts with inner & outer curved surfaces:
92 C
93       A = X(4)**2 + X(5)**2 - X(6)**2*TANTHS
94       B = X(1)*X(4) + X(2)*X(5) - X(3)*X(6)*TANTHS
95  
96       DO 38 NCYL =1,2
97         C = R2 - X(3)**2*TANTHS - PAR(NCYL)**2
98         SURD = B**2 - A*C
99         IF(SURD.GT.0.) THEN
100           SURD=SQRT(SURD)
101           DIST1=(-B+SURD)/A
102           IF(DIST1.GT.0.) SNXT=MIN(SNXT,DIST1)
103           DIST2=(-B-SURD)/A
104           IF(DIST2.GT.0.) SNXT=MIN(SNXT,DIST2)
105 C       not necessary to compute intercept with outer surface
106 C       if there is a positive intercept with inner surface:
107           IF(DIST1.GT.0. .OR. DIST2.GT.0.) GO TO 999
108         ENDIF
109   38  CONTINUE
110 C
111  999  CONTINUE
112       END