# Find spatial prediction-error filter.
#
subroutine pe2( eps, a1,a2,aa, n1,n2 ,pp, rr, niter, jump)
integer              a1,a2,    n1,n2,         niter, jump
integer i1, iter, midpt, r12, a12
real	aa( a1 , a2),  pp( n1 , n2),  rr( n1 , n2 * 2),  eps
temporary real da( a1, a2),  dr( n1, n2 * 2)
temporary real sa( a1, a2),  sr( n1, n2 * 2)
r12 = n1 * n2
a12 = a1 * a2
call null( aa, a12);	call null( rr, 2 * r12)
call null( da, a12);	call null( dr, 2 * r12)
midpt = (a1+1) / 2
aa( midpt, 1 ) = 1.
	call cinjof( 0, 0, jump, n1,n2,pp, a1,a2,aa, rr         )
	call ident ( 0, 0, eps,            a12,  aa, rr(1,n2+1) )
	call scale (       -1.,		 2*r12,      rr         )
do iter= 0, niter {
	call cinjof( 1, 0, jump, n1,n2,pp, a1,a2,da, rr         )
	call ident ( 1, 1,  eps,           a12,  da, rr(1,n2+1) )
	do i1= 1, a1 { 				 da(i1, 1) = 0. }
	call cinjof( 0, 0, jump, n1,n2,pp, a1,a2,da, dr         )
	call ident ( 0, 0,  eps,           a12,  da, dr(1,n2+1) )
	call cgstep( iter,   a12, aa,da,sa,
			   2*r12, rr,dr,sr )
	}
return; end