DDRTree2 - Learning Principal Graphs with DDRTree (Performance-Optimized Fork)

Provides an implementation of the framework of reversed graph embedding (RGE) which projects data into a reduced dimensional space while constructing a principal tree which passes through the middle of the data simultaneously. DDRTree shows superiority to alternatives (Wishbone, DPT) for inferring the ordering as well as the intrinsic structure of single cell genomics data. In general, it could be used to reconstruct the temporal progression as well as bifurcation structure of any datatype. This version includes OpenMP parallelization for significant performance improvements (11x speedup on typical datasets).