Navigability evaluation of complex networks by greedy routing efficiency
An important characteristic of any network is its navigability. The navigability of a network embedded in a geometrical space is associated with the fact that greedy routing (GR) performed using the node geometrical coordinates is efficient (1⇓⇓⇓–5). In PNAS, Seguin et al. (6) define a measure for quantifying the efficiency of brain network navigability in the Euclidean space, referred to as the efficiency ratio, whose formula exactly coincides with the GR-score previously introduced by Muscoloni et al. (7). However, in contrast to Muscoloni et al. (7), the study of Seguin et al. (6) ( i ) proposes the efficiency ratio without referring to GR at all, ( ii ) provides no rationale for the introduction of the efficiency ratio with respect to the two main GR measures already adopted in the literature, and ( iii ) does not discuss any advantage of the measure, nor does it explain that the efficiency ratio in fact integrates the two former measures. Therefore, we feel that, for … 

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