This function similate differential expression fold change level
fcsim(n.gene, de.id, fc.loc, fc.scale)total number of genes
index of differentially expressed genes
location parameter for fold change (log-normal distribution)
scale parameter for fold change (log-normal distribution)
Zappia, L., Phipson, B., & Oshlack, A. (2017). Splatter: Simulation of single-cell RNA sequencing data. Genome Biology, 18(1). https://doi.org/10.1186/s13059-017-1305-0