Linear Algebra and Its Applications, cilt.737, ss.1-16, 2026 (SCI-Expanded, Scopus)
In this paper, we establish necessary and sufficient matrix conditions for polynomial sequences to be d-orthogonal and classical d-orthogonal. Our approach employs a matrix method developed by Verde-Star [46], which we extend to characterize d-orthogonality. Moreover, as an application of our framework, the 2-orthogonality of linear combinations of consecutive polynomials is examined, illustrating how these matrix conditions can be utilized in practice. An example constructed with the help of the Tchebychev 2-orthogonal polynomials of the second kind is also established.