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STOCHASTIC

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(d) Show that Q„ is nonempty and consists of positive-semidefinite and positivedefinite<br />

matrices of order mxm.<br />

(e) Suppose 0. e \J„^mQ„(Z). Show that V(-, •,£) = V(-, -,il). [Hint: Utilize (c) and<br />

work with independent standardized normal variates in n space.]<br />

(f) Show that for all k i,..., k„, there exists a A:* such that<br />

K(-,-,L) = V(-,-,{au + kt + kj + k*}).<br />

The result in (f) indicates a framework for the definition of a class of surrogate functions<br />

that are analytically convenient. Since V(-,-,£) is essentially identical to V(-,-,il) if<br />

£ I e Qm (X), a natural surrogate family is defined as<br />

g(x,l,Q) = gfon^au + ki + kj + k*})<br />

= 2 log Xx, exp [ft, + i(! + Mj + i(ff« + OJJ + 2

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