On Rotational Symmetries of Drawings of Coherent Periodic Graphs

Periodic graphs are used to model crystals. The symmetry of crystal structure is one of the important subjects. A symmetric drawing of the periodic graphs reveals the symmetry of a crystal structure. In this paper, we present a necessary condition so that a drawing, where the edges can be drawn by general curves, of a coherent periodic graph can admit the translational symmetry and the rotational symmetry.