The sum of squared logarithms inequality

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)=1j1<j2<<jknyj1yj2yjk.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,,n1),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=1nlog2aii=1nlog2bi.\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 nNn\in\mathbb N is the open issue.

Sources & referencesView supporting material

Primary source

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

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