The function calculates the column totals and divides each value within the column by the respective column total.
This function calculates the relative abundance of each feature in the SummarizedExperiment object containing count data, expressed as counts per million (CPM)
relativeAb(se, assay = 1L)
returns a new SummarizedExperiment object with counts per million calculated and added as a new assay named rel_abs.