c_EdgeListFromSegList   Turn a segment list into an edgelist suitable
                        for constructing an ngraph
c_ListofMatrixRows      Convert a matrix into list of row vectors
c_coords21dindex        Convert physical coordinates to 1d indices into
                        image array
c_ijkpos                Convert physical coordinates to pixel
                        coordinates
c_listlengths           A simple function to compute the lengths of the
                        elements of an R list
c_seglengths            Compute summed segment lengths or total cable
c_sub2ind               Find 1D index given n-dimensional indices
c_topntail              Find the first and last elements of all vectors
                        in a list
