David J. Clements

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A solution X of a discrete-time algebraic Riccati equation is called unmixed if the corresponding closed-loop matrix Φ(X) has the property that the common roots of det (sI − Φ(X)) and det (I − sΦ(X) *) (if any) are on the unit circle. A necessary and sufficient condition is given for existence and uniqueness of an unmixed solution such that the eigenvalues(More)
The only string models known to reproduce the Minimal Supersymmetric Standard Model in the low energy effective field theory are those constructed in the free fermionic formulation. We demonstrate the existence of quasi– realistic free fermionic heterotic–string models in which supersymmetric singlet flat directions do not exist. This raises the possibility(More)
We revisit the singular control problem and obtain new numerical and theoretical results. The advantage of the obtained numerical algorithm is that it is robust in respect to the numerical inaccuracy, which is due to a numerical rounding. Indeed, if some incorrect FGEs are extracted due to the numerical inaccuracy instead of the correct IGEs, then we reject(More)
We present a control design to solve the global output feedback stabilization problem of a class of uncertain nonlinear systems. Each system in this class consists of some dynamic uncertainties, linear parametric uncertainties and, most importantly, output-dependent uncertain integrator gains or virtual coefficients. To solve the problem, an observer design(More)
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