  Double parton distribution functions (DPDFs) are used in the QCD description
of double parton scattering. The DPDFs evolve with hard scales through
relatively new QCD evolution equations which obey nontrivial momentum and
valence quark number sum rules. Based on the constructed numerical program, we
present results on the QCD evolution of the DPDFs. In particular, we discuss
the problem how to specify initial conditions for the evolution equations which
exactly fulfill the sum rules.
