PROGRAM EXAMPLE
C  This example makes the ray-tracing procedure for a single 
C  user defined ray within the user defined Winston Cone
	IMPLICIT DOUBLE PRECISION (A-H,O-Z)
        DIMENSION X0(2),V0(3),X1(2),V1(3)
        TIN=2.0   ! entrance diameter of the Winston Cone
	TOUT=0.653         ! exit diameter of the Winston Cone
	RR=1.49         ! ratio between internal and external 
C                         refractive indeces
c	RR=0.           ! if RR.le.1 100% reflection independent of 
C                         incidence angle
	NMAX=20         ! maximum allowed # of bounces for a single ray
        CALL WICOIN(TIN,TOUT,RR,NMAX,ELLE)
	PRINT*,' Winston Cone LENGTH =',ELLE
C-------  loop on input data
	X0(1)=2.    ! input coordinate of the user defined ray
	X0(2)=1.
	V0(1)=0.1    ! input direction of the user defined ray
	V0(2)=0.1    ! not necessarily a unit vector
	V0(3)=-1.    ! (it is normalized inside WICO)
	CALL WICO(X0,V0,X1,V1,D,N,IERR)
	IF(IERR.EQ.1)PRINT*,'ray impact point out of entrance face: IERR=1'
	IF(IERR.EQ.2)PRINT*,'number of bounces greater than NMAX: IERR=2'
	IF(IERR.EQ.3)PRINT*,' the ray comes back to the entrance face:IERR=3'
	IF(IERR.EQ.4)PRINT*,' ray incident out of limit angle:IERR=4'
	IF(IERR.EQ.0)THEN
	  PRINT*,' photon transmitted - IERR=0'
          PRINT*,' output coordinate',X1(1),X1(2)
          PRINT*,' output direction',V1(1),V1(2),V1(3)
          PRINT*,' total path length',D
          PRINT*,' total number of bounces',N
        ENDIF
	STOP
	END