First, many thanks to Simon Urbanek for his help. A simulation case (50x34x5x3 & 250 replications) each based on behavior of 2500 consumers takes - 2h20mins on a laptop (2 MHz, 1Go, WinXp) - 1h on a G5 bi-proc (2.5 Mhz, 2Go) A loop was used for the laptop, the same loop was transposed as function for the Mac Best regards Naji