M. Mohr Constantin Popa U. Rüde An iterative algorithm for approximate orthogonalisation of symmetric matrices. 215-226 2004 81 Int. J. Comput. Math. 2 http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=0020-7160&volume=81&issue=2&spage=215 db/journals/ijcm/ijcm81.html#MohrPR04