grandes-ecoles 2013 Q9a

grandes-ecoles · France · x-ens-maths2__mp Proof Direct Proof of a Stated Identity or Equality
For all $n \in \mathbf{N}$, let $S_{n} f$ be the function of $\mathcal{C}_{0}$ defined by $$S_{n} f = \sum_{j=0}^{n} \sum_{k \in \mathcal{T}_{j}} c_{j,k}(f) \theta_{j,k}$$ Show that for all $n \in \mathbf{N}$ and all $\ell \in \mathcal{T}_{n+1}$, the function $S_{n} f$ is affine on the interval $[\ell 2^{-n-1}, (\ell+1) 2^{-n-1}]$.
For all $n \in \mathbf{N}$, let $S_{n} f$ be the function of $\mathcal{C}_{0}$ defined by
$$S_{n} f = \sum_{j=0}^{n} \sum_{k \in \mathcal{T}_{j}} c_{j,k}(f) \theta_{j,k}$$
Show that for all $n \in \mathbf{N}$ and all $\ell \in \mathcal{T}_{n+1}$, the function $S_{n} f$ is affine on the interval $[\ell 2^{-n-1}, (\ell+1) 2^{-n-1}]$.