Interchanging a limit and an integral: necessary and sufficient conditions

Necessary and Sufficient Conditions for Differentiating under the Integral Sign

an 2 00 1 Necessary and sufficient conditions for differentiating under the integral sign

a f(x, y) dy, it is often important to know when F is differentiable and when F (x) = ∫ b a f1(x, y) dy. A sufficient condition for differentiating under the integral sign is that ∫ b a f1(x, y) dy converges uniformly; see [6, p. 260]. When we have absolute convergence, the condition |f1(x, y)| ≤ g(y) with ∫ b a g(y) dy < ∞ suffices (Weierstrass M-test and Lebesgue Dominated Convergence). If we...

Extending Peano derivatives: necessary and sufficient conditions

The paper treats functions which are defined on closed subsets of [0, 1] and which are k times Peano differentiable. A necessary and sufficient condition is given for the existence of a k times Peano differentiable extension of such a function to [0, 1]. Several applications of the result are presented. In particular, functions defined on symmetric perfect sets are studied.

Necessary and Sufficient Conditions for Copositive Tensors

In this paper, it is proved that a symmetric tensor is (strictly) copositive if and only if each of its principal subtensors has no (non-positive) negative H++-eigenvalue. Necessary and sufficient conditions for (strict) copositivity of a symmetric tensor are also given in terms of Z++-eigenvalues of the principal sub-tensors of that tensor. This presents a method for testing (strict) copositiv...

Necessary and sufficient conditions for quantum computation

Necessary and sufficient conditions are given for a quantummechanical system to possess a coordinate system with respect to which its behaviour at discrete times is that of a universal digital computer . The form of the diagonal representation for the unitary time evolution operator for quantum universal computers is derived ; aspects of the transformation between the diagonal representation an...