I have a QP problem of the following kind:
$\min_{\alpha\in\mathbb{R}^n}\frac{1}{2}\alpha^T M \alpha - p^T\alpha$
s.t. $l\leq \alpha \leq u$
The matrix $M$ is symmetric and positive definite and of a special structure, such that for each submatrix M_{I,I}, $I \subset \{1,...,n\}$ I can calculate both $M_{I,I} x$ and $M_{I,I}^{-1}x$ in $\mathcal{O}(\#I)$ operations on a single core. Which algorithm will probably be most efficient to solve this until a given epsilon precision, and scales well with increasing $n$.
So far I have a coordinate descent that scales $n^2$ which is probably pretty inefficient.