Halting space-bounded computations

Unambiguous Logarithmic Space Bounded Computations

On the Derandomization of Space-Bounded Computations

Some Observations about Relativization of Space Bounded Computations

In this column we explore what relativization says about space bounded computations and what recent results about space bounded computations say about relativization. There is a strong belief in computational complexity circles that problems which can be relativized in two contradictory ways are very hard to solve. We believe that such problems can only be solved by proof techniques that do not...

Space Bounded Computations: Review And New Separation Results

In this paper we review the key results about space bounded complexity classes, discuss the central open problems and outline the prominent proof techniques. We show that, for a slightly modified Turing machine model, low level deterministic and nondeterministic space bounded complexity classes are different. Furthermore, for this computation model, we show that Savitch’s theorem and the Immerm...

Trading Determinism for Time in Space Bounded Computations

Savitch showed in 1970 that nondeterministic logspace (NL) is contained in deterministic O(log n) space but his algorithm requires quasipolynomial time. The question whether we can have a deterministic algorithm for every problem in NL that requires polylogarithmic space and simultaneously runs in polynomial time was left open. In this paper we give a partial solution to this problem and show t...