 Anisotropic renormalization group

A renormalization-group transformation can scale different coordinate directions by different factors to keep distinct gradient terms fixed. If momentum component $p_i$ scales to $b^{w_i}{p}_i$, its coordinate scales by $b^{-w_i}$. The momentum/volume measure has total scaling weight ${\sum }_i{w}_i$, motivating the anisotropic effective dimension.