Inverse-chi-square quadratic-form conjecture for weighted normal reciprocals

From papers

Let X=(X1,X2,,Xk)TNk(0,Σ)X=(X_1,X_2,\ldots,X_k)^T\sim\mathcal{N}_k(0,\Sigma), with none of its entries a point mass. Let p1,p2,,pnp_1,p_2,\ldots,p_n be nonnegative numbers satisfying

p1+p2++pn=1.p_1+p_2+\cdots+p_n=1.

Inverse-chi-square conjecture. Then

(p1X1,p2X2,,pnXn)Σ(p1X1,p2X2,,pnXn)T1χ12.\left(\frac{p_1}{X_1},\frac{p_2}{X_2},\ldots,\frac{p_n}{X_n}\right)\Sigma \left(\frac{p_1}{X_1},\frac{p_2}{X_2},\ldots,\frac{p_n}{X_n}\right)^T \sim\frac{1}{\chi^2_1}.

The paper presents this as an equivalent reciprocal formulation of the weighted-ratio Cauchy conjecture. Its notation uses kk for the dimension of XX but nn for the number of weights, so that indexing should be checked against the source.

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Sources & referencesView supporting material

Primary source

Mathias Drton and Han Xiao, “Wald tests of singular hypotheses”, arXiv:1304.6746 (2016).

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