function [res] = invheat(lambda)global A U D V bdeltan = size(A,2);% compute regularized solutionw       = diag(D)./(diag(D).^2 + lambda*ones(size(diag(D))));xlambda = V*(w.*(U(:,1:n)'*bdelta));res     = norm(bdelta-A*xlambda) - 1.e-3*norm(bdelta);