George Biros Omar Ghattas Parallel Lagrange-Newton-Krylov-Schur Methods for PDE-Constrained Optimization. Part I: The Krylov-Schur Solver. 687-713 2005 27 SIAM J. Sci. Comput. 2 https://doi.org/10.1137/S106482750241565X db/journals/siamsc/siamsc27.html#BirosG05