# Kirchhoff dip-moveout and modelling.  (tutorial, slow)
#
subroutine  kdmoslow(   conj, add, v,     h, t0,dt,dx, nt,nx,   p0,   pn)
integer ix,iy,it,iz,nz, conj, add,                     nt,nx
real x0,y0,dy,z0,dz,tn,x,y,z,hs,   v,     h, t0,dt,dx,   p0(nt,nx),   pn(nt,nx)
real r,tnmx,wgt,tmax
call conjnull(          conj, add,                       p0,nt*nx,    pn,nt*nx)
x0=0.;  y0=0;  dy=dx;  z0=t0;  dz=dt; nz=nt; tmax=t0+(nt-1)*dt
wgt = 1.
if( h != 0. )
	wgt = dx / h
do ix= 1, nx {  x = x0 + dx * (ix-1)
do iy= 1, nx {  y = y0 + dy * (iy-1)
	hs = abs((x-y) / h)
 	if( hs > 0.999) goto 10		# avoid sqrt of negative
	r = sqrt( 1. - hs * hs)
	if( hs != 0. )
	   tnmx = 2 * h / v * r / hs    # cutoff at 90-degree dip
	else
	   tnmx = tmax
	tnmx = min(tnmx,tmax)		
do it= 1, nt {  tn= t0 + dt * (it-1)	# tn = finite-offset time after NMO
 	if( tn > tnmx ) break
	z = tn * r    			#  z = zero-offset time
	iz = 1.5 + (z-z0) / dz
		if( conj == 0 )
			  pn(it,iy) =   pn(it,iy) +   p0(iz,ix) * wgt
		else
			  p0(iz,ix) =   p0(iz,ix) +   pn(it,iy) * wgt
	}
10	continue
	}}
return; end