# Phase shift modeling and migration.   (Warning: destroys its input!)
#
subroutine gazconj( conj, dt,dx, v,nt,nx, modl,         data )
integer	            conj,          nt,nx,			 iw, ikx, iz,nz
complex	eiktau, cup, 	                  modl(nt,nx),  data(nt,nx)
real	                  dt,dx, v(nt),              pi, w,w0,dw, kx,kx0,dkx,qi
call conjnull(     conj,  0,              modl,nt*nx*2, data,nt*nx*2 )
pi = 4.*atan(1.);	w0  = -pi/dt;	dw = 2.*pi/(nt*dt);    qi=.5/(nt*dt)
nz = nt;		kx0 = -pi/dx;	dkx= 2.*pi/(nx*dx)
if( conj == 0)	call ft2axis( 0, -1., nz, nx, modl)
else	{	call ft2axis( 0, -1., nt, nx, data)
	  	call ft1axis( 0,  1., nt, nx, data)
		}
do ikx  = 2, nx     {       kx = kx0 + (ikx-1) * dkx
do iw   = 2, 1+nt/2 {       w  = w0  + (iw -1) * dw
	if( conj== 0) { data(iw,ikx) = modl(nz,ikx)
		do iz = nz-1, 1, -1 
			data(iw,ikx) = data(iw,ikx) * eiktau(dt,w,v(iz)*kx,qi) +
				       modl(iz,ikx)
		}
	else {		cup          = data(iw,ikx)
		do iz = 1, nz {
			modl(iz,ikx) = modl(iz,ikx)  +  cup
			cup          = cup *  conjg(  eiktau(dt,w,v(iz)*kx,qi))
			}
		}
	}}
if( conj == 0)  { call ft1axis( 1,  1., nt, nx, data)
		  call ft2axis( 1, -1., nt, nx, data) }
else            { call ft2axis( 1, -1., nz, nx, modl) }
return; end