Consider a function
K(x,y) continuously differentiable in x ∈ Rn and y ∈ Rm. We form two
problems:
PRIMAL: Find (x,y) ≧ 0 and Min F such that
DUAL: Find (x,y) ≧ 0 and Max G such that
where DyK(x,y) and DxK(x,y) denote the vectors of partial derivatives DyiK(x,y)
and DxjK(x,y) for i = 1,⋯,m and j = 1,⋯,n. Our main result is the existence of a
common extremal solution (x0,y0) to both the primal and dual systems when (i) an
extremal solution (x0,y0) to the primal exists, (ii) K is convex in x for each y,
concave in y for each x and (iii) K, twice differentiable, has the property
at (x0,y0) that its matrix of second partials with respect to y is negative
definite.
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