# Difference between revisions of "P=NP implies a deterministic algorithm to find primes"

(New page: Consider the decision problem of determining whether there is a prime in the range <math>[m,n]</math>, where <math>m < n</math>. This problem is in NP, since if there is a prime in the ra...) |
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− | Consider the decision problem of determining whether there is a prime in the range <math>[m,n]</math>, where <math>m < n</math>. This problem is in NP, since if there is a prime in the range, we can efficiently verify that it is prime. By assumption, this decision problem is therefore in P, | + | Consider the decision problem of determining whether there is a prime in the range <math>[m,n]</math>, where <math>m < n</math>. This problem is in NP, since if there is a prime in the range, we can efficiently verify that it is prime. By assumption, this decision problem is therefore in P, i.e., there is a polynomial-time algorithm to determine whether there is a prime in the range <math>[m,n]</math>. |

We can use this algorithm as a subroutine to quickly find a prime in the range [n,2n] for large n. We use the well-known fact that such a prime always exists. We then use the polynomial-time algorithm described above to do a binary search to locate such a prime. This terminates after at most <math>\log_2 n</math> applications of the subroutine, and thus is a polynomial-time algorithm to generate a prime. | We can use this algorithm as a subroutine to quickly find a prime in the range [n,2n] for large n. We use the well-known fact that such a prime always exists. We then use the polynomial-time algorithm described above to do a binary search to locate such a prime. This terminates after at most <math>\log_2 n</math> applications of the subroutine, and thus is a polynomial-time algorithm to generate a prime. |

## Revision as of 21:26, 28 July 2009

Consider the decision problem of determining whether there is a prime in the range [math][m,n][/math], where [math]m \lt n[/math]. This problem is in NP, since if there is a prime in the range, we can efficiently verify that it is prime. By assumption, this decision problem is therefore in P, i.e., there is a polynomial-time algorithm to determine whether there is a prime in the range [math][m,n][/math].

We can use this algorithm as a subroutine to quickly find a prime in the range [n,2n] for large n. We use the well-known fact that such a prime always exists. We then use the polynomial-time algorithm described above to do a binary search to locate such a prime. This terminates after at most [math]\log_2 n[/math] applications of the subroutine, and thus is a polynomial-time algorithm to generate a prime.