... no means fortuitous but follows from the principleof energy conservation and from its corollary, the well-known Maxwell±Bettireciprocal theorem.EALcos2 sin cos ÿcos2 ÿsin cos ... the computation.It is a simple matter to transform the coordinates of the displacement and forcecomponents of Eq. (1.3) to any other coordinate system. Clearly, it is necessary todo so before ... assumed.If now the equilibrium conditions of a typical node, i, are to be established, eachcomponent of rihas, in turn, to be equated to the sum of the component forcescontributed by the elements...