EPOM is an R package implemented based on the paper Epigenome overlap measure (EPOM) for comparing tissue/ cell types based on chromatin states by Wei Vivian Li, Zahra S. Razaee and Jingyi Jessica Li (2016).
Before using the package, you can check EPOM-vignette.pdf and EPOM.pdf.
epom_func_test.R will also be a good reference.