@article{etna_vol41_pp13-20, author = {Andreas G\"unnel and Roland Herzog and Ekkehard Sachs}, title = {A note on preconditioners and scalar products in Krylov subspace methods for self-adjoint problems in Hilbert space}, journal = {Electron. Trans. Numer. Anal.}, volume = {41}, year = {2014}, pages = {13--20}, }