The sum of squared logarithms inequality

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Let a1,a2,…,ana_1,a_2,\ldots,a_n and b1,b2,…,bnb_1,b_2,\ldots,b_n be positive numbers. For k∈{1,2,…,n}k\in\{1,2,\ldots,n\}, define the standard elementary symmetric polynomials

ek(y1,…,yn)=∑1≤j1<j2<…<jk≤nyj1yj2⋯yjk.e_k(y_1,\ldots,y_n)=\sum_{1\le j_1<j_2<\ldots<j_k\le n}y_{j_1}y_{j_2}\cdots y_{j_k}.

Sum of squared logarithms inequality. If

ek(a1,…,an)≤ek(b1,…,bn)(k=1,2,…,n−1),en(a1,…,an)=en(b1,…,bn),e_k(a_1,\ldots,a_n)\leq e_k(b_1,\ldots,b_n)\quad(k=1,2,\ldots,n-1),\qquad e_n(a_1,\ldots,a_n)=e_n(b_1,\ldots,b_n),

then

∑i=1nlog⁡2ai≤∑i=1nlog⁡2bi.\sum_{i=1}^n\log^2a_i\leq\sum_{i=1}^n\log^2b_i.

The inequality was known for n=2,3n=2,3 when this conjecture was formulated, and the source reports support from random sampling for small nn; its validity for arbitrary n∈Nn\in\mathbb N is the open issue.

References

Primary source

Waldemar Pompe and Patrizio Neff, “On the generalized sum of squared logarithms inequality”, arXiv:1410.2706 (2015).

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