[1] KTH, NADA, Trasko Storo Inst Math, S-10044 Stockholm, Sweden
[2] Univ Nacl Cordoba, Fac Matemat Astron & Fis, RA-5000 Cordoba, Argentina
[3] Univ Nacl Cordoba, IFEG, RA-5000 Cordoba, Argentina
[4] Lawrence Livermore Natl Lab, Ctr Appl Sci Comp, Livermore, CA USA