Stoll M, Wathen A (2011) Preconditioning for partial differential equation constrained optimization with control constraints. Numerical Linear Algebra with Applications 19: 53–71. Available: http://dx.doi.org/10.1002/nla.823.
The first author would like to thank Tyrone Rees and Nick Gould for sharing their knowledge. The authors would also like to thank the anonymous referee for helping to improve this publication. This publication is partially based on work supported by Award No. KUK-C1-013-04, made by King Abdullah University of Science and Technology (KAUST).