function A1 = collapse(A,merge,tha)
[m,m] = size(A);
keep = setdiff(1:m,merge);
A0 = [A(keep,:); sum(A(merge,:),1)];
THA = repmat(tha(:)',[length(keep)+1 1]);
A1 = [A0(:,keep) sum(A0(:,merge).*THA,2)];
return