optional; path to defined cell cycle genes. Default uses gene sets defined in Kowalczyk, M. S. et al. Single-cell RNA-seq reveals changes in cell cycle and differentiation programs upon aging of hematopoietic stem cells. Genome Res 25, 1860-1872, doi:10.1101/gr.192237.115 (2015).
Value
a matrix of cell cycle genes activation scores (S, G2M and aggregated S/G2M scores, separately)