Marsden dual functional
= Marsden dual functional
{c}
The Marsden dual functionals extract coefficients in a <B-spline> expansion. If $\psi_i$ is the knot polynomial in the <Marsden identity>, then on polynomials of degree at most $k-1$ one such functional is
$$
\lambda_i(p)=\sum_{j=0}^{k-1}(-1)^j\psi_i^{(k-1-j)}(x)p^{(j)}(x),
$$
and the right-hand side is independent of $x$.