A '''galactic algorithm''' is an [[algorithm]] with record-breaking theoretical ([[Asymptotic computational complexity|asymptotic]]) performance, but which isn'tis not used due to practical constraints. Typical reasons are that the performance gains only appear for problems that are so large they never occur, or the algorithm's complexity outweighs a relatively small gain in performance. Galactic algorithms were so named by [[Richard Lipton]] and Ken Regan,<ref name="seminal">{{cite book |last1=Lipton |first1=Richard J. |author-link1=Richard Lipton|first2=Kenneth W. |last2=Regan |chapter=David Johnson: Galactic Algorithms |title=People, Problems, and Proofs: Essays from Gödel's Lost Letter: 2010 |publisher=Springer Berlin |___location=Heidelberg |year=2013 |pages=109–112 |chapter-url=https://books.google.com/books?id=eLC9BAAAQBAJ&pg=PA109 |isbn=9783642414220}}</ref> because they will never be used on any data sets on Earth.
