function [ac,zm]=acform(m,ph,pv,overlap)
% ACFORM builds the coarse-level operator. 
%
% function [ac,zm]=acform(m,ph,pv,overlap)
%
global at
op=overlap;
[lv,rv]=partition(m,pv,op);
[lh,rh]=partition(m,ph,op);
%zm=zeros(m*m,ph*pv);
zm=sparse([],[],[],m*m,ph*pv,3*m*m);
h=1/(m+1);
%ac=zeros(ph*pv,ph*pv);
%at=pmat2(m,m,h);
for ih=1:ph
	lbh=lh(ih); ubh=rh(ih); lenh=ubh-lbh+1; 
	for iv=1:pv
		zb=zeros(m,m); zi=zeros(m*m,1);
		i=ih+ph*(iv-1);
                lbv=lv(iv); ubv=rv(iv); lenv=ubv-lbv+1;
		%		zb(lbh:ubh,lbv:ubv)=1; 
		zb(lbh:ubh,lbv:ubv)=pu(lenh,lenv,overlap);
		zi=zb(:);ni=norm(zi,2); zi=zi/ni;
		zm(:,i)=zi; 
	end
end
ac=zm'*(at*zm);