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This paper is mainly concerned with a two-species competition model in open advective environments, where individuals cannot pass through the upstream boundary and do not return to the habitat after leaving the downstream boundary. By the theory of principal eigenvalue, we first obtain two critical curves (Γ1 and Γ2) in the plane of bifurcation parameters that sharply determine the local stability of the two semitrivial steady states. Then under various conditions on given parameters, we discuss the global dynamics via different techniques, including the comparison principle for eigenvalues and perturbation and compactness arguments, and show that both competitive exclusion and coexistence are possible. For general values of parameters, we take both analytic and numerical approaches to further understand the potential behaviors of Γ1 and Γ2, and we numerically observe that in addition to the competitive exclusion and coexistence, the bistable phenomenon is also possible, which is different from the known results of competitive ODE and reaction-diffusion systems (where bistability is impossible). The implication of our numerical results on future work is also discussed. [ABSTRACT FROM AUTHOR]

In this paper, we consider the generalized eigenvalue problem (GEP) for bidiagonalproduct (BP) pairs with sign regularity (SR), which include structured pairs associated with illconditioned matrices, such as Cauchy and Vandermonde matrices, that arise in many applications. A sufficient and necessary condition is provided for an SR-BP pair to be regular. For regular SR-BP pairs having both matrices singular, we establish sharp relative perturbation bounds to show that all the generalized eigenvalues including infinite and zero ones can be accurately determined by their BP representations. By operating on the BP representations, a new method is developed to accurately compute generalized eigenvalues of such a regular SR-BP pair. Our method first transforms the pair into an equivalent pair with a certain sign regularity. Then a technique is proposed to implicitly deflate all the infinite eigenvalues. After deflating infinite eigenvalues, finite eigenvalues are computed by reducing the deflated GEP into a standard eigenvalue problem. An attractive property of our method is that all the generalized eigenvalues are returned to high relative accuracy especially, all the infinite and zero eigenvalues are computed exactly. Error analysis and numerical experiments are performed to confirm the claimed high relative accuracy. [ABSTRACT FROM AUTHOR]

We analyze the recently introduced family of preconditioners in [M. M. Rana et al., SIAM J. Sci. Comput., 43 (2021), pp. S475-S495] for the stage equations of implicit Runge--Kutta methods for s-stage methods. We simplify the formulas for the eigenvalues and eigenvectors of the preconditioned systems for a general s-stage method and use these to obtain convergence rate estimates for preconditioned GMRES for some common choices of the implicit Runge-Kutta methods. This analysis is based on understanding the inherent matrix structure of these problems and exploiting it to qualitatively predict and explain the main observed features of the GMRES convergence behavior, using tools from approximation and potential theory based on Schwarz--Christoffel maps for curves and close, connected domains in the complex plane. We illustrate our analysis with numerical experiments showing very close correspondence of the estimates and the observed behavior, suggesting the analysis reliably captures the essence of these preconditioners. [ABSTRACT FROM AUTHOR]