Relaxation and numerical approximation of a two-fluid two-pressure diphasic model Annalisa Ambroso, Christophe Chalons, Frédéric Coquel and Thomas Galié ESAIM: M2AN, 43 6 (2009) 1063-1097 Published online: 09 October 2009 DOI: 10.1051/m2an/2009038