Hello!
"u" is the vector containing coordinates of points sewing. The quantity of points sewing is not any size and there should be always on n-1 less, than a quantity of experimental points. Also on coordinates of points sewing are imposed a following condition: the first point sewing should be not more to the right of the first experimental point, and last not more to the left of last experimental point. Other points sewing can place arbitrarily in a segment.
Example in Mathcad 15:
P.S. Also, the information on function "bspline" can be found in "Mathcad Help", having pressed key F1.
