The chain topology parameter (CTP) is defined by
Where nr is the number of residues in a protein, nc is the number of inter-residue contacts and DLij is the sequence separation between the contacting residues i and j in the protein sequence (Nolting et al., 2003). The weighted implementation of this index in ProtDCal is as follow:
Nolting, B., Schalike, W., Hampel, P., Grundig, F., Gantert, S., Sips, N., Bandlow, W., and Qi, P.X., 2003. Structural determinants of the rate of protein folding. J. Theor. Biol. 223, 299-307.