1UPMC Univ Paris 06, UMR 7623, LIP, F-75005 Paris, France
2CNRS, UMR 7623, Laboratoire d’Imagerie Paramétrique, F-75005 Paris, France
3Department of Structural Mechanics, University of Granada, 18071 Granada, Spain
4School of Mathematics, Alan Turing Building, University of Manchester, Manchester, M13 9PL, UK