Wayne Eberly Mark Giesbrecht Pascal Giorgi Arne Storjohann Gilles Villard Faster Inversion and Other Black Box Matrix Computations Using Efficient Block Projections http://arxiv.org/abs/cs/0701188 2007 CoRR abs/cs/0701188 db/journals/corr/corr0701.html#abs-cs-0701188 informal publication