PYTHIA is a program for the generation of high-energy physics events, i.e.
for the description of collisions at high energies between elementary
particles such as e⁺, e⁻, p and p̄ in various combinations. It contains
theory and models for a number of physics aspects, including hard and soft
interactions, parton distributions, initial and final-state parton showers,
multiple interactions, fragmentation and decay.
