  Expanding medium is very common in many different fields, such as biology and
cosmology. It brings a nonnegligible influence on particle's diffusion, which
is quite different from the effect of an external force field. The dynamic
mechanism of particle's motion in expanding medium has only been investigated
in the framework of continuous-time random walk. To focus on more diffusion
processes and physical observables, we build the Langevin picture of anomalous
diffusion in expanding medium, and conduct detailed analyses in the framework
of Langevin equation. With the help of a subordinator, both subdiffusion
process and superdiffusion process in expanding medium are discussed. We find
that the expanding medium with different changing rate (exponential form and
power-law form) leads to quite different diffusion phenomena. The particle's
intrinsic diffusion behavior also plays an important role. Our detailed
theoretical analyses and simulations present a panoramic view of investigating
anomalous diffusion in expanding medium under the framework of Langevin
equation.
