The sum of the eigenvalues {λn} of an operator is usually called its trace. For the eigenvalues λn of an differential operator, the series \({\sum_n \lambda_n}\) , generally speaking, diverges; however, it can be regularized by subtracting from λn the first terms of the asymptotic expansion, which interfere with the convergence of the series. The sum of such a regularized series is called the trace. In this work, we consider the spectral problem for Sturm–Liouville differential operator on d-star-type graph with a Kirchhoff-type condition in the internal vertex, where the integer d ≥ 2. Regularized trace formula of this operator is established with residue techniques in complex analysis.
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