Determinant Dynamics under Low-Rank Perturbations: A Unified Framework for Singular Systems

TL;DR

This paper introduces a comprehensive framework for analyzing how determinants and related spectral properties evolve under low-rank perturbations, applicable to both invertible and singular matrices, with implications for control theory.

Contribution

It develops a unified, adjugate-based approach extending classical identities to singular matrices using Drazin inverse and pseudodeterminant, linking perturbation theory with system concepts.

Findings

Derived explicit formulas for determinant evolution under rank-one updates.

Extended classical identities to singular matrices using Drazin inverse.

Analyzed eigenvalue shifts and stability conditions under low-rank perturbations.

Abstract

This paper develops a unified analytical framework for determinant identities under finite-rank perturbations of square matrices that remains valid without invertibility assumptions. In contrast to classical inverse-based formulations, the approach is based on an adjugate-driven additive representation, which extends naturally to singular matrices and yields explicit, non-asymptotic formulas. Building on this representation, we derive recursive and multiplicative expressions describing the evolution of determinant and log-determinant quantities under successive rank-one updates. These results reveal a structural interpretation in which determinant-based quantities evolve as cumulative measures of independent directions, providing a precise decomposition of incremental contributions. To address the singular case, we develop a systematic extension based on the Drazin inverse and the pseudodeterminant, leading to closed-form identities that isolate the contribution of the nonzero spectrum. In particular, we obtain a generalized determinant formula that can be viewed as a singular counterpart of the matrix determinant lemma. The spectral impact of low-rank perturbations is analyzed, yielding explicit conditions governing eigenvalue shifts and stability preservation. The proposed framework establishes a direct analytical link between matrix perturbation theory and system-theoretic concepts. In particular, we show that the pseudodeterminant of controllability Gramians admits a multiplicative decomposition that explicitly quantifies the incremental expansion of the reachable subspace under successive inputs. This leads to a unified interpretation of information accumulation, uncertainty reduction, and reachability in both full-rank and rank-deficient linear systems.