\begin{definition}[Definition:Ritz Method]
Let $\MM$ be a normed linear space.
Let $J\sqbrk y$ be a functional defined on space $\MM$.
Let $\sequence{\phi_n}$ be an infinite sequence of mappings in $\MM$.
Let $\MM_n$ be an $n$-dimensional linear subspace of $\MM$, spanned by first $n$ mapping of $\sequence{\phi_n}$.
Let $\eta_n = \boldsymbol \alpha \boldsymbol \phi$, where $\boldsymbol \alpha$ is a real $n$-dimensional vector.
Minimise $J \sqbrk {\eta_n}$ {{WRT}} $\boldsymbol\alpha$.
Then $J \sqbrk {\eta_n}$ is an approximate minimum of $J \sqbrk y$, and is denoted by $\mu_n$.
This method is known as '''Ritz method'''.
\end{definition}