This R code in this package is distributed under the GPL-3 license.  It is free,
open source, and has the following attribution requirements
(GPL Section 7):

(a) you agree to retain in 'ndtv' and any modifications to 'ndtv'
    the copyright, author attribution and URL information as
    provided at http://statnet.org/attribution
(b) you agree that 'ndtv' and any modifications to 'ndtv' will,
    when used, display the attribution:
     Based on 'statnet' project software (http://statnet.org).
     For license and citation information see http://statnet.org/attribution