## 3. A simple element analysis (cont'd)

This functional is the one to be minimized using the Rayleigh-Ritz procedure.

As for what basis functions to use, the simplest choice is a set which permits the displacement field over the element to be a general linear function of $$x$$ and $$y$$. For this, three basis functions are needed.

There are two ways of formulating them, one based on Cartesian coördinates and the other on so-called ‘natural’ coördinates. The ultimate result is the same, but in some circumstances one of the two formulations may be superior.

R. Funnell