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arXiv · 2410.17123

Pythagoras Numbers for Ternary Forms

Grigoriy Blekherman·Alex Dunbar·Rainer Sinn
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Abstract

We study the Pythagoras numbers $py(3,2d)$ of real ternary forms, defined for each degree $2d$ as the minimal number $r$ such that every degree $2d$ ternary form which is a sum of squares can be written as the sum of at most $r$ squares of degree $d$ forms. Scheiderer showed that $d+1\leq py(3,2d)\leq d+2$. We show that $py(3,2d) = d+1$ for $2d = 8,10,12$. The main technical tool is Diesel's characterization of height 3 Gorenstein algebras.

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Grigoriy Blekherman, Alex Dunbar, Rainer Sinn. 2024-10-22. Pythagoras Numbers for Ternary Forms. https://arxiv.org/abs/2410.17123

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