Before revision: We consider the problem of computing  \sum_x e^{f(x)}, where f (x)=\sum_{ij a_{ij} \xi_i \xi_j + \sum_i b_i \xi_i is a real-valued quadratic function and x=} \xi_1, \ldots, \xi_n ranges over{\Bbb   the Boolean cube \{-1, 1\}^n.
After revision: We consider the problem of computing the partition function \sum_x e^{f(x)}, where f (x)=\sum_{ij a_{ij} \xi_i \xi_j + \sum_i b_i \xi_i is a real-valued quadratic function and x=} \xi_1, \ldots, \xi_n ranges over{\Bbb the Boolean cube \{-1, 1\}^n.