Fig. 6

Four realizations of removed basis functions using on the stiffness matrix based selection procedure described in “Interpolation error estimates” section; all using the same constant \(c=0.01\) for the tolerance \(tol = ch^{p} \times \sqrt{E}\) in (51). Each cross marks a removed basis function and the domain of its support is visualized in pink. In (a)–(c) we note that the selection becomes more restrictive with smaller mesh size h. Comparing (b) and (d) we also note that more basis functions typically may be removed as the spline order increases. a \(C^1Q^2\), \(h=0.4\). b \(C^1Q^2\), \(h=0.2\). c \(C^1Q^2\), \(h=0.1\). d \(C^2Q^3\), \(h=0.2\)