A stability of Oseen flow by circular cylinder is investigated. The work has methodical character. Rvachev function is applied for illustrating possibilities of the method. The authors build the structure that satisfies the boundary conditions and represents approximately solution. Unknown factors were found by a collocation method. The flow is stable in the field of applicability of the Oseen formula. The method is simple and exponentially converging.

Key words: hydrodynamic stability, Oseen flow, partial differential equations, spectral methods.