The Publisher regrets that this article is an accidental duplication of an article that has already been published in MLBLUE, 138 (2015) 259–261, http://dx.doi.org/10.1016/j.electacta.2014.10.094. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.