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math.OC2026

Sum of Squares Rank of Biquadratic Forms and The Zarankiewicz Number

Chunfeng Cui, Liqun Qi, Yi Xu

Denote the maximum sos rank of sum of squares (SOS) biquadratic forms by . In this paper, we show that and conjecture that $BSR(m, n…

math.OC2026

Sum of Squares Decompositions and Rank Bounds for Biquadratic Forms

Liqun Qi, Chunfeng Cui, Yi Xu

We study SOS properties of biquadratic forms. For the class of partially symmetric biquadratic forms, we establish necessary and sufficient conditions for positive semi-definitenes…

math.OC2025

Sum of Squares Decompositions for Structured Biquadratic Forms

Yi Xu, Chunfeng Cui, Liqun Qi

This paper studies sum-of-squares (SOS) representations for structured biquadratic forms. We prove that diagonally dominated symmetric biquadratic tensors are always SOS. For the s…

math.OC2025

Structured Symmetric Tensors

Liqun Qi, Chunfeng Cui, Yi Xu

In this paper, we study structured symmetric tensors. We introduce several new classes of structured symmetric tensors: completely decomposable (CD) tensors, strictly sum of square…

math.OC2025

A Dual Quaternion Control Law for Formation Control of Multiple 3-D Rigid Bodies

Chunfeng Cui, Liqun Qi, Hao Chen +1

This paper studies the integrated position and attitude control problem for multi-agent systems of 3D rigid bodies. While the state-of-the-art method in [Olfati-Saber and Murray, 2…

math.OC2025

Postive Semidefinite and Sum of Squares Biquadratic Polynomials

Chunfeng Cui, Liqun Qi, Yi Xu

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…