PROPER ORTHOGONAL DECOMPOSITION OF DLA CLUSTERS

We use the proper orthogonal decomposition to analyze the fluctuations around the mean of DLA clusters gown in a sector. These fluctuations are described as a superposition of orthogonal modes, which appear to have very well-defined shapes. These modes are invariants of the growt h, and show a strong selection phenomenon which is reflected in the la rge-scale structure of the branching pattern of DLA clusters. We also discuss the appearance of discrete scale invariance.