C+
C NAME:
C	nrTrapZD
C PURPOSE:
C CATEGORY:
C CALLING SEQUENCE:
	subroutine nrTrapZD(Func,A,B,S,N)
C INPUTS:
C OUTPUTS:
C CALLS:
C	Say, Choose, nrPolInt
C EXTERNAL:
C INCLUDE:
C COMMON BLOCKS:
C SIDE EFFECTS:
C RESTRICTIONS:
C PROCEDURE:
C	See Numerical Recipes
C MODIFICATION HISTORY:
C	JUN-1993, Paul Hick (UCSD)
C-
	    real	Func
	    real	A
	    real	B
	    real	S
	    integer	N

	save	IT

	BA = B-A
	if (N .eq. 1) then
	    S = 0.5*BA*(Func(A)+Func(B))
	    IT = 1			! # points added on next call
	else
	    TNM = IT
	    DEL = BA/TNM		! Spacing of points to be added
	    X = A+0.5*DEL
	    SUM = 0.
	    do J=1,IT
		SUM = SUM+Func(X)
		X = X+DEL
	    end do
	    S = 0.5*(S+BA*SUM/TNM)	! Refined S value
	    IT = 2*IT
	end if

	return
	end