Kinematic and vertex fitting package for the CMD-3 experiment

In this article, we discuss a new software package of kinematic and vertex fitting for the CMD-3 experiment at the VEPP-2000 electron-positron collider. The authors describe in detail the fitting algorithm, parametrization of four-momenta and trajectories of various particles and present the results of testing the fitting pakage using events of Monte Carlo simulation of various e + e - annihilation processes. The authors also provide several examples of the fitting package validation using Gaussian simulation. Although the package discussed in this article is intended for the CMD-3 experiment, it can also be used in other experiments. The authors consider the described package as their first step towards a more universal and rigorous kinematic and vertex fitting package that can be used in future e + e - experiments, such as the Super Charm-Tau factory.