 smoothing data with periodic and parametric
       splines, Computer Graphics and Image Processing, vol. 20, p. 171 (1982).
       :doi:`10.1016/0146-664X(82)90043-0`

.. [2] Tom Lyche and Knut Morken, Spline methods,
    http://www.uio.no/studier/emner/matnat/ifi/INF-MAT5340/v05/undervisningsmateriale/

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