15 e 290 teoremi

15 e 290 theorems In mathematics, il 15 theorem or Conway–Schneeberger Fifteen Theorem, proved by John H. Conway and W. UN. Schneeberger in 1993, states that if a positive definite quadratic form with integer matrix represents all positive integers up to 15, then it represents all positive integers.[1] The proof was complicated, and was never published. Manjul Bhargava found a much simpler proof which was published in 2000.[2] Bhargava used the occasion of his receiving the 2005 SASTRA Ramanujan Prize to announce that he and Jonathan P. Hanke had cracked Conway's conjecture that a similar theorem holds for integral quadratic forms, with the constant 15 replaced by 290. [3] The proof has since appeared in preprint form.[4] Details Suppose {stile di visualizzazione Q_{ij}} is a symmetric matrix with real entries. For any vector {stile di visualizzazione x} with integer components, definire {stile di visualizzazione Q(X)=somma _{io,j}Q_{ij}X_{io}X_{j}} This function is called a quadratic form. We say {stile di visualizzazione Q} is positive definite if {stile di visualizzazione Q(X)>0} Ogni volta che {displaystyle xneq 0} . Se {stile di visualizzazione Q(X)} is always an integer, we call the function {stile di visualizzazione Q} an integral quadratic form.

We get an integral quadratic form whenever the matrix entries {stile di visualizzazione Q_{ij}} sono numeri interi; poi {stile di visualizzazione Q} is said to have integer matrix. Tuttavia, {stile di visualizzazione Q} will still be an integral quadratic form if the off-diagonal entries {stile di visualizzazione Q_{ij}} are integers divided by 2, while the diagonal entries are integers. Per esempio, x2 + xy + y2 is integral but does not have integral matrix.

A positive integral quadratic form taking all positive integers as values is called universal. Il 15 theorem says that a quadratic form with integer matrix is universal if it takes the numbers from 1 a 15 as values. A more precise version says that, if a positive definite quadratic form with integral matrix takes the values 1, 2, 3, 5, 6, 7, 10, 14, 15 (sequence A030050 in the OEIS), then it takes all positive integers as values. Inoltre, for each of these 9 numbers, there is such a quadratic form taking all other 8 positive integers except for this number as values.

Per esempio, the quadratic form {displaystyle w^{2}+x^{2}+si^{2}+z^{2}} is universal, because every positive integer can be written as a sum of 4 squares, by Lagrange's four-square theorem. By the 15 teorema, to verify this, it is sufficient to check that every positive integer up to 15 is a sum of 4 squares. (This does not give an alternative proof of Lagrange's theorem, because Lagrange's theorem is used in the proof of the 15 teorema.) D'altro canto, {displaystyle w^{2}+2x^{2}+5si^{2}+5z^{2},} is a positive definite quadratic form with integral matrix that takes as values all positive integers other than 15.

Il 290 theorem says a positive definite integral quadratic form is universal if it takes the numbers from 1 a 290 as values. A more precise version states that, if an integer valued integral quadratic form represents all the numbers 1, 2, 3, 5, 6, 7, 10, 13, 14, 15, 17, 19, 21, 22, 23, 26, 29, 30, 31, 34, 35, 37, 42, 58, 93, 110, 145, 203, 290 (sequence A030051 in the OEIS), then it represents all positive integers, and for each of these 29 numbers, there is such a quadratic form representing all other 28 positive integers with the exception of this one number.

Bhargava has found analogous criteria for a quadratic form with integral matrix to represent all primes (il set {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 67, 73} (sequence A154363 in the OEIS)) and for such a quadratic form to represent all positive odd integers (il set {1, 3, 5, 7, 11, 15, 33} (sequence A116582 in the OEIS)).

Expository accounts of these result have been written by Hahn[5] and Moon[6] (who provides proofs).

References ^ Conway, J.H. (2000). "Universal quadratic forms and the fifteen theorem". Quadratic forms and their applications (Dublin, 1999) (PDF). Contemp. Matematica. vol. 272. Provvidenza, RI: Amer. Matematica. soc. pp. 23–26. ISBN 0-8218-2779-0. Zbl 0987.11026. ^ Bhargava, Manjul (2000). "On the Conway–Schneeberger fifteen theorem". Quadratic forms and their applications (Dublin, 1999) (PDF). Contemp. Matematica. vol. 272. Provvidenza, RI: Amer. Matematica. soc. pp. 27–37. ISBN 0-8218-2779-0. SIG 1803359. Zbl 0987.11027. ^ Alladi, Krishnaswami. "Ramanujan's legacy: the work of the SASTRA prize winners". Philosophical Transactions of the Royal Society A. The Royal Society Publishing. Recuperato 4 febbraio 2020. ^ Bhargava, M., & Hanke, J., Universal quadratic forms and the 290-theorem. ^ Alexander J. Hahn, Quadratic Forms over {displaystyle mathbb {Z} } from Diophantus to the 290 Teorema, Advances in Applied Clifford Algebras, 2008, Volume 18, Issue 3-4, 665-676 ^ Yong Suk Moon, Universal quadratic forms and the 15-theorem and 290-theorem Categories: Additive number theoryTheorems in number theoryQuadratic forms