C+
C NAME:
C	ArrR8Interpolate
C PURPOSE:
C	Interpolate on 1-dim double precision array.
C CALLING SEQUENCE:
	double precision function ArrR8Interpolate(N,A,X)
C INPUTS:
C	N	integer			# points in array
C	A(N)	double precision	Array of function values 
C	X	double precision	Function value where interpolated position is needed
C OUTPUTS:
C	ArrR8Interpolate
C		double precision	interpolated index in [1,N]
C					A BadR4 value is returned if X lies outside the
C					range of input array A.
C CALLS:
C	BadR8
C RESTRICTIONS:
C	A must be a monotonically increasing array.
C PROCEDURE:
C	For given X the pair of indices I-1 and I are located
C	where A(I-1) < X <= A(I). Then a linear interpolation between these
C	two points gives the return floating point index.
C MODIFICATION HISTORY:
C	OCT-2003, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
C-
	    integer		N
	    double precision	A(*)
	    double precision	X

	double precision	BadR8

	if (A(1) .le. X .and. X .le. A(N)) then

	    I = 1
	    do while (I .le. N .and. X .gt. A(I))
		I = I+1
	    end do

	    ArrR8Interpolate = dble(I)
	    if (I .ne. 1) ArrR8Interpolate = ArrR8Interpolate-(X-A(I))/(A(I-1)-A(I))

	else

	    ArrR8Interpolate = BadR8()

	end if

	return
	end