Greville abscissa (${\xi }_i=\frac{1}{k-1}{\sum }_{r=1}^{k-1}{t}_{i+r}$)

For an order-$k$ B-spline with $k\ge 2$, its Greville abscissa is the arithmetic mean of its $k-1$ interior knots. These are precisely the coefficients reproducing the linear function in the monomial B-spline coefficients formula. The irregular plural is Greville abscissae.