“The Fastest and Shortest Algorithm for All Well-Defined Problems”, 2002-06-14 (; backlinks):
An algorithm M is described that solves any well-defined problem p as quickly as the fastest algorithm computing a solution to p, save for a factor of 5 and low-order additive terms.
M optimally distributes resources between the execution of provably correct p-solving programs and an enumeration of all proofs, including relevant proofs of program correctness and of time bounds on program runtimes. M avoids Blum’s speed-up theorem by ignoring programs without correctness proof. M has broader applicability and can be faster than Levin’s universal search, the fastest method for inverting functions save for a large multiplicative constant.
An extension of Kolmogorov complexity and two novel natural measures of function complexity are used to show that the most efficient program computing some function f is also among the shortest programs provably computing f.