c_ ---------------------------------------------------------------------
c_ RCS lines preceded by "c_ "
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c_
c_ $Source: /home/orr/WWW/Abiotic/boundcond/RCS/locate.f,v $ 
c_ $Revision: 1.1 $
c_ $Date: 1999/04/26 13:52:31 $   ;  $State: Exp $
c_ $Author: orr $ ;  $Locker:  $
c_
c_ ---------------------------------------------------------------------
c_ $Log: locate.f,v $
c_ Revision 1.1  1999/04/26 13:52:31  orr
c_ Initial revision
c_
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c_ 
      SUBROUTINE locate(xx,n,x,j)

c     From Numerical recipes:
c     -----------------------
c     Given an array XX of length N, and a given value of X, returns a
c     value of J such that X is between XX(J) and XX(J+1).  XX must be
c     monotonic, either increasing or decreasing. J=0 or J=N is
c     returned to indicate that X is out of range.      

      DIMENSION xx(n)
      jl=0
      ju=n+1
 10   IF(ju-jl.gt.1)THEN
          jm=(ju+jl)/2
          IF((xx(n).gt.xx(1)).eqv.(x.gt.xx(jm)))THEN
              jl=jm
          ELSE
              ju=jm
          ENDIF
          go to 10
      ENDIF
      j=jl
      RETURN
      END