[1] CSIC, Inst Estruct Mat, Serrano 123, Madrid 28006, Spain
[2] Univ Carlos III Madrid, Grp Modelizac Simulac Numer Matemat Ind, Avda Univ 30, Leganes 28911, Spain
[3] Univ Carlos III Madrid, Grp Teorias Campos & Fis Estat, Inst Gregorio Millan, Unidad Asociada Inst Estruct Mat,CSIC, Madrid, Spain