Thomas J. Laffey

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In t h i s paper we desor ibe a program t h a t v e r i f i e s t he oons is tenoy and completeness of exper t system knowledge bases whioh u t i l i z e t he Lookheed Expert System (LES) framework. The a l g o r i t h m s desor ibed here are not s p e c i f i c to LES and oan be a p p l i e d to most r u l e -based systems. The program, o a l l e d CHECK,(More)
complex applications such as satellite control, autonomy, and data analysis; the Pilot's Associate; autonomous vehicles; battle management; aerospace systems (for example, monitoring electric, power, propulsion, and life-support systems); communications network monitoring and control; robotics and vision systems; process control; financial advice (for(More)
Dedicated to Hans Schneider on the occasion of his seventieth birthday. Abstract. Let A be an entrywise nonnegative n n matrix and let sk := trace (A) (k = 1;2; : : :). It is shown that if n is odd and s1 = 0, then (n 1)s4 s22. The result is applied to show that (3; 1 2 (1 p17); 2; 2) is not the spectrum of a nonnegative 5 5 matrix while (3; 1 2 (1 p 17);(More)
We show that there exist real numbers λ1, λ2, . . . , λn that occur as the eigenvalues of an entry-wise nonnegative n-by-n matrix but do not occur as the eigenvalues of a symmetric nonnegative n-by-n matrix. This solves a problem posed by Boyle and Handelman, Hershkowitz, and others. In the process, recent work by Boyle and Handelman that solves the(More)
Let F be a field, Mn(F ) the algebra of n × n matrices over F and A ∈ Mn(F ) with trace(A) = 0. The following facts are well-known (i) if A is not a scalar, then A is similar over F to a matrix with zero diagonal (ii) A = [P, Q] = PQ − QP for some P , Q ∈ Mn(F ). In this paper we consider the situation when F is replaced by the ring of integers Z. We show(More)