In accordance with the random walk model, the end to end vector average vanishes due to symmetry considerations. Therefore, in order to get an estimate of the polymer size, we turn to the end to end vector variance : ⟨ R → → 2 ⟩ = N l 2 with the end to end vector defined as: R → → ≡ ≡ ∑ ∑ n = 1 N r → → n .