Patent ID: 8223908

Claim:
A method, comprising: identifying, by an apparatus, an optimal root index in a first domain according to a first performance criterion; determining, by the apparatus, a domain-dual root index for the optimal root index in the first domain and computing a performance metric for the domain-dual root index; and when the domain-dual root index satisfies a second performance criterion, storing, by the apparatus, the optimal root index; wherein said step of identifying an optimal root index in a first domain further comprises computing a performance metric for a set of indices in the first domain and wherein the performance metric is ∑ k = - N / 2 1 ⁢ ( kl λ ⁡ ( k ) ) - 2 + ∑ k = 1 N / 2 - 1 ⁢ ( kl λ ⁡ ( k ) ) - 2 , ⁢ where l λ ⁡ ( k ) = - λ ⁢ ⁢ k ⁡ ( mod ⁢ ⁢ N ) - N / 2.