# signal advance:    y(iy) = x(iy+jump)
#
subroutine advance( conj, add, jump, nx, xx, ny, yy)
integer ix, iy,     conj, add, jump, nx,     ny
real 					 xx(nx), yy(ny)
call conjnull( conj, add,                xx,nx,  yy,ny)
do iy= 1, ny {
	ix = iy + jump
	if(         ix >= 1 )
		if( ix <= nx )
			if( conj == 0 )
				yy( iy) = yy( iy) + xx( ix)
			else
				xx( ix) = xx( ix) + yy( iy)
	}
return; end