%0 Journal Article %T Stable Flags and the Riemann-Hilbert Problem %A Eduardo Corel %A Elie Compoint %J Mathematics %D 2010 %I arXiv %X We tackle the Riemann-Hilbert problem on the Riemann sphere as stalk-wise logarithmic modifications of the classical R\"ohrl-Deligne vector bundle. We show that the solutions of the Riemann-Hilbert problem are in bijection with some families of local filtrations which are stable under the prescribed monodromy maps. We introduce the notion of Birkhoff-Grothendieck trivialisation, and show that its computation corresponds to geodesic paths in some local affine Bruhat-Tits building. We use this to compute how the type of a bundle changes under stalk modifications, and give several corresponding algorithmic procedures. %U http://arxiv.org/abs/1003.5021v1