cepip - Cell Explanatory Power with Inflection Point (CEP-IP) with CMRF

Implements the cell explanatory power with inflection point (CEP-IP) framework for single-cell co-expression analysis. A generalized additive model (GAM) fitted by restricted maximum likelihood (REML) with a penalized residual sum of squares (PRSS) search over the basis dimension relates a gene of interest to the mean of its partner genes. Cells are ranked by their explanatory power, and the inflection point is the first negative-to-positive zero crossing of a residual GAM. Optional extensions are the Spearman-Kendall cell-level score (SKCS) and the copula monotone recovery filter (CMRF), which recovers cells near the module through a tolerance band and a repeated stratified k-fold cross-validation gate. Downstream helpers give per-donor module fractions, paired donor-level differential expression and donor-level association models. CEP-IP is described in Wong (2026) <doi:10.1016/j.cmpb.2026.109372>.