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Calculate the natural modes of a cyclic symmetric structure.

The generalized components of the eigenmodes of the entire structure are calculated, by a cyclic substructuring method, from the modal base of a reference sector (cf. [:ref:`R4.06.03 <R4.06.03>`]). The axis of symmetry is the OZ axis. The sector's modal base must be of type CLASSIQUE. Interfaces DROITE, GAUCHE and possibly AXE must be of the same type. The right and left sides are defined by the trigonometric direction in plane OXY.

Produces a mode_cycl data structure.