  Circumstellar discs, from which planetary systems are formed, consist of gas,
dust and solids. Simulations of self-consistent dynamics of gas, dust and
solids in circumstellar discs is a challenging problem. In the paper we present
fast algorithms for computing the drag force (momentum transfer) between solid
phase and gas. These algorithms (a) are universal and applicable to dust and
solids with any sizes smaller than the mean free path of gas molecules, (b) can
be used to calculate the momentum transfer between dust and gas instead of
one-way effect, as it is done in many models, (c) can perform simulations,
without a loss in accuracy, with the time step determined by gas-dynamic
parameters rather than by drag force, and (d) are compatible with the widely
used parallel algorithms for solving 3D equations of gas dynamics, hydrodynamic
equations for dust, and the collisionless Boltzmann equation for large bodies.
Preliminary results of supercomputer simulation of the gas-dust disc dynamics
within the developed approach are reported.
