Methods of Nonlinear Analysis (Enhanced Edition‪)‬

In Volume I, we discussed the Bubnov-Galerkin and Rayleigh-Ritz
methods, both procedures for transforming the task of solving a given
equation into that of minimizing a specified functional. By means of a
suitably chosen sequence of trial functions and algebraic operations we
could obtain a decreasing sequence of upper bounds for the desired
minimum value, and thus derive an approximation to the solution of
the original equation.