Dragon2. A novel code for cosmic-ray transport in the Galaxy

We introduce Dragon2, the new version of the public software package designed to study cosmic-ray propagation in the Galaxy. Our aim is to illustrate the approach followed in the writing of the code and to present its most important features. We describe the properties of the numerical scheme that has been adopted in Dragon2 to implement the different processes related to cosmic-ray transport and we investigate its correctness by comparing our numerical results with a set of analytical solutions. Starting from these validation tests, we study in detail the performances of the code by probing the different factors that influence its accuracy and its speed under a wide range of different conditions. Lastly, we investigate the new features introduced in Dragon2 in the treatment of diffusion, energy losses and reacceleration and their impact on the predicted fluxes, in comparison also with the results given by the previous version of the code.