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   A Block Orthogonalization Procedure with Constant Synchronization
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   https://epubs.siam.org/doi/10.1137/S1064827500370883
[DuerschEtal2018] Jed A. Duersch, Meiyue Shao, Chao Yang, Ming Gu.
   (2018) A Robust and Efficient Implementation of LOBPCG. SIAM J.
   Sci. Comput., 40(5), C655-C676. (22 pages)
   https://epubs.siam.org/doi/abs/10.1137/17M1129830