Positive Semi-Definite and Sum of Squares Biquadratic Polynomials

Hilbert proved in 1888 that a positive semi-definite (PSD) homogeneous quartic polynomial of three variables always can be expressed as the sum of squares (SOS) of three quadratic polynomials, and a psd homogeneous quartic polynomial of four variables may not be sos. Only after 87 years, in 1975, Ch...

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Bibliographic Details
Main Authors: Chunfeng Cui, Liqun Qi, Yi Xu
Format: Article
Language:English
Published: MDPI AG 2025-07-01
Series:Mathematics
Subjects:
Online Access:https://www.mdpi.com/2227-7390/13/14/2294
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