SUBROUTINE Bisect(r, v, rleft, vleft, rright, vright, delta)
USE Numeric_Kinds_Module
IMPLICIT NONE
!==============================================================================
! This subroutine determines if the bounds need to be shifted higher or
!   lower in order to find the exact point at which the potential is equal
!   to vasy
!==============================================================================
REAL(dp) :: r, v, rleft, vleft, rright, vright, delta

 IF(vleft*v.lt.0.d0)THEN 
   rright=r      
   vright=v
 ELSEIF(vleft*v.gt.0.d0)THEN  
   rleft=r        
   vleft=v
 ELSE         
   rleft=r
   vleft=v
   rright=r
   vright=v
 ENDIF
 r=(rleft+rright)/2.d0       
 delta=ABS(rright-rleft)/r  

 RETURN
 END SUBROUTINE Bisect