This imbedding of an ‘almost symmetrical' problem into a ‘truly symmetrical' (equivariant) one is a simple idea, but what exactly its scope and limitations are is not clear as yet. One should like to have a classification of all structures to which this process can be applied. This is an open question which seems to request some ‘pure' (if not very deep) mathematics in order to be settled. 3.2 . Symmetry alterations Again in order to emphasize the idea, let us introduce a simple example, even though it is only remotely related to space structures. Consider (Fig. 7) an elastic membrane of uniform thickness, with its edges fixed to a rigid horizontal frame. The shape is that of an equilateral triangle. Suppose some stiffener X is stuck somewhere on the surface. A load / is given, and one wants the vertical deflexion. If there was no stiffener, the problem would be formulated (after some discretization process) as where A is the stiffness matrix of the membrane alone. This is an equivariant problem, so one could apply the theory. (The group, here, has 6 elements).
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