  The speed-gradient variational principle (SG-principle) is formulated and
applied to thermodynamical systems. It is shown that Prigogine's principle of
minimum entropy production and Onsager's symmetry relations can be interpreted
in terms of the SG-principle and, therefore, are equivalent to each other. In
both cases entropy of the system plays a role of the goal functional. The
speed-gradient formulation of thermodynamic principles provide their extended
versions, describing transient dynamics of nonstationary systems far from
equilibrium. As an example a model of transient (relaxation) dynamics for
maximum entropy principle is derived.
