## Japan Journal of Industrial and Applied Mathematics

- Japan J. Indust. Appl. Math.
- Volume 24, Number 3 (2007), 229-239.

### Efficient Verification of Tunnell's Criterion

#### Abstract

An integer $n$ is congruent if there is a triangle with rational sides whose area is $n$. In the 1980s Tunnell gave an algorithm to test congruence which relied on counting integral points on the ellipsoids $2x^2+y^2+8z^2 = n$ and $2x^2+y^2+32z^2=n$. The correctness of this algorithm is conditional on the conjecture of Birch and Swinnerton-Dyer. The known methods for testing Tunnell's criterion use $O(n)$ operations. In this paper we give several methods with smaller exponents, including a randomized algorithm using time $n^{1/2 + o(1)}$ and space $n^{o(1)}$, and a deterministic algorithm using space and time $n^{1/2 + o(1)}$.

#### Article information

**Source**

Japan J. Indust. Appl. Math. Volume 24, Number 3 (2007), 229-239.

**Dates**

First available in Project Euclid: 17 December 2007

**Permanent link to this document**

http://projecteuclid.org/euclid.jjiam/1197909110

**Mathematical Reviews number (MathSciNet)**

MR2374988

**Zentralblatt MATH identifier**

1183.11015

**Keywords**

congruent numbers quadratic forms class field theory algorithms complexity

#### Citation

Bach, Eric; Ryan, Nathan C. Efficient Verification of Tunnell's Criterion. Japan J. Indust. Appl. Math. 24 (2007), no. 3, 229--239. http://projecteuclid.org/euclid.jjiam/1197909110.