where τ is the "hard" threshold parameter. Thus, two genes are linked (aij = 1) if the absolute correlation between their expression profiles exceeds the (hard) threshold τ. The hard-thresholding procedure is implemented in the function signumAdjacencyFunction. While unweighted networks are widely used, they do not reflect the continuous nature of the underlying co-expression information and may thus lead to an information loss. In contrast, weighted networks allow the adjacency to take on continuous values between 0 and 1. A weighed network adjacency can be defined by raising the co-expression similarity to a power [5,10]:
