This function detects the optimal number of transcription factors which are regulating each target gene. This number is different for different target genes. It utilizes a heuristic to also detect the isolated targets which are not regulated by any transcription factor. To the detect the optimal number of Tfs for each target gene, it uses a notion similar to that used for optimization of the L-curve criterion for Tikonov regularization by evaluating the variable importance curve for each target gene.