  Convection-diffusion problem are the base for continuum mechanics. The main
features of these problems are associated with an indefinite operator the
problem. In this work we construct unconditionally stable scheme for
non-stationary convection-diffusion equations, which are based on use of new
variables. Also, we consider these equations in the form of
convection-diffusion-reaction and construct unconditionally stable schemes when
explicit-implicit approximations are used with splitting of the reaction
operator.
