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)