Typical dynamical evolution of a population of planetary embryos in two different simulations. In both plots, the horizontal axis represents the time and the vertical one shows the semimajor axis. The upper panel shows the dynamical evolution of three planetary embryos or cores of 10 M_⊕ each. The lower panel shows the dynamical evolution of a numerous population of 20 planetary embryos of 1.5 M_⊕ each. In both simulations the gas lasts 9 Myr.