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    Active Circuits With Diodes: Topological Conditions Sufficient to Determine the State of a Diode

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    Let N be a circuit composed of a finite number of positive and negative linear resistors, ideal diodes, nullators, norators and independent current and voltage sources. In this article, we consider the problem to determine, without any numerical computation, the state of a diode of N. We propose a set of topological conditions such that, when verified by a diode of N, the state of the diode is determined and the same in all the solutions of N. Our results may simplify, sometimes dramatically, the usual trial-and-error procedure to find the solutions of N

    A note on smooth matrices of constant rank

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    We show that, given a ChC^h time–varying matrix A(t) of constant rank, there exists a ChC^h matrix H(t) such that the rows of H(t)A(t) are an orthonormal basis of the space spanned by the rows of A(t). We present some consequences of this result and, in particular, we prove a version for m×nm \times n matrices of Doležal's Theorem. These results are not new, and references are given. All the proofs of the results stated in these references, with the exception of those based on the use of differential equations — which holds only for h1h \geq 1 —, find suitable ChC^h matrices defined on overlapping subsets of the domain and then patch them together without losing regularity and the other required properties. In our approach the patching needs to be done only for matrices consisting of one row and all the remaining results are obtained by usual algebraic tools
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