def __init__(self, datapoints, t = None, c = None, k = 3, bokeps = 2.0, boktests = 5, bokwindow = None, plotcolour="black"):
		"""
		t : all the knots (not only internal ones !)
		c : corresponding coeffs
		k : degree : default = cubic splines k=3 -> "order = 4" ???
		whatever ... 3 means that you can differentiate twice at the knots.