Criterion of determination of order of Galerkin's approximation of decision of initially boundary value problems

On account of analysis of the functional of Lyapounov's type constructed for partial differential equation, describing of the plate free vibrations, the absolute and uniform convergence of the approximate decisions of this equations obtained by the Galerkin's method to the exact decision is proved. The criterion of determination of order of approximate decision for the finding of exact decision with given accuracy is obtained. The developed criterion is maybe used under constructing of the decisions of broad class of others linear partial differential equations.