Reduction (complexity) - Examples

Examples

  • To show that a decision problem P is undecidable we must find a reduction from a decision problem which is already known to be undecidable to P. That reduction function must be a computable function. In particular, we often show that a problem P is undecidable by showing that the halting problem reduces to P.
  • The complexity classes P, NP and PSPACE are closed under polynomial-time reductions.
  • The complexity classes L, NL, P, NP and PSPACE are closed under log-space reduction.

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