[G+smo] Greville abscissae

The Greville abscissae are defined to be the mean location of k-1 consecutive knots in the knot vector for each basis spline function of order k. Note that the first and last knots in the knot vector are excluded when applying this definition; consequently there are gsl_bspline_ncoeffs Greville abscissa. They are often used in B-spline collocation applications and may also be called Marsden-Schoenberg points.

        gsMatrix<> ct;
        m_patches.basis(0).anchors_into(ct);