Figure 3.

Nonzero BB coefficients ● of the basis function $f_{21}^{\ell }$. The coefficient marked additionally with an × is nonzero only for $f_{21}^{\ell }$. It is zero for $f_{12}^k$ or $f_{11}^k$, k = 0, …, n − 1 and for $f_{21}^k$, k ≠ ℓ.