; twodw.pro
; Based on TWODW.FR
;
; Revisions:
;	2001 Nov 5 - rgf - IDL version
;
;***file twodw.fr
;**dick french
;***latest revision 5/29/81
;
;---this fortran 5 routine is used in program golc.  it computes the
;   integrand used for determination of the bending angle for
;   two-dimensional waves using geometric optics.  see rgf mit#3 p.128+.
;   note that this program can be easily generalized to handle any
;   two-dimensional refractivity profile.
;
;
function twodw,ha,i,j,dxhat,hhat,eps,wlpsh, $
	psi,rhat,shphw,beta,del,idiag

	twopi=!dpi*2.d0
	zkhat=twopi*wlpsh
	zlhat=twopi/shphw
	xj=double(j)*dxhat
	rdif=ha+xj*xj/(2.d0*rhat) - double(i-1)/hhat
	earg=zkhat*rdif+psi
	darg=zlhat*xj+beta
	ce=cos(earg)
	se=sin(earg)
	cd=cos(darg)
	sd=sin(darg)
	ex=exp(-rdif)
	znu=ex*(1.d0 + eps*se + del*cd)
	dndr=-znu + ex*eps*zkhat*ce
	dndx=-ex*del*zlhat*sd
	twodw=dndr-xj*dndx
	if(idiag eq 0)then return,twodw
	print, "j=",j," znu=",znu
	print, "zkhat=",zkhat," zlhat=",zlhat
	print, "earg=",earg," darg=",darg
	print, "ce=",ce," se=",se
	print, "cd=",cd," sd=",sd
	print, "ex=",ex," del=",del
	print, "dndr=",dndr," dndx=",dndx
	print, "xj=",xj," rdif=",rdif
	print, "twodw=",twodw
	print
	return,twodw
	end