code: def support_false_positive_count(m, m_hat):
      
      m_nnz, m_hat_nnz, intersection_nnz = _nonzero_intersection(m, m_hat)
      return int((m_hat_nnz - intersection_nnz) / 2.0)
docs: Count the number of false positive support elements in
      m_hat in one triangle, not including the diagonal.