Luca Bergamaschi Angeles Martinez Giorgio Pini Parallel preconditioned conjugate gradient optimization of the Rayleigh quotient for the solution of sparse eigenproblems. 1694-1715 2006 175 Applied Mathematics and Computation 2 http://dx.doi.org/10.1016/j.amc.2005.09.015 db/journals/amc/amc175.html#BergamaschiMP06