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This paper develops theory for a newly-defined bicomplex hyperbolic harmonic function with four real-dimensional inputs, in a way that generalizes the connection between real harmonic functions with two real-dimensional inputs and complex analytic functions. For example, every bicomplex hyperbolic harmonic function appears as this paper's newly-defined hyperbolic real part of a bicomplex analytic function, just as every real harmonic function with two real-dimensional inputs is the real part of a complex analytic function. In addition, this connection produces a unique (up to additive constant) and newly-defined hyperbolic harmonic conjugate function, just as every real harmonic function has a unique (up to additive constant) real harmonic conjugate. Finally, the paper determines a bicomplex Poisson kernel function that produces a corresponding integral representation for bicomplex harmonic functions, one that generalizes the complex harmonic function Poisson integral representation., Comment: 8 pages, 1 figure

Given an n by n matrix A over the complex numbers and an invariant subspace L, this paper gives a straightforward formula to construct an n by n matrix N that commutes with A and has L equal to the kernel of N. For Q a matrix putting A into Jordan canonical form J = RAQ with R the inverse of Q, we get N = RM$ where the kernel of M is an invariant subspace for J with M commuting with J. In the formula M = P ZVW with V the inverse of a constructed matrix T and W the transpose of P, the matrices Z and T are m by m and P is an n by m row selection matrix. If L is a marked subspace, m = n and Z is an n by n block diagonal matrix, and if L is not a marked subspace, then m > n and Z is an m by m near-diagonal block matrix. Strikingly, each block of Z is a monomial of a finite-dimensional backward shift. Each possible form of Z is easily arranged in a lattice structure isomorphic to and thereby displaying the complete invariant subspace lattice L(A) for A., Comment: 12 pages with two illustrations of invariant subspace lattice diagrams

This paper extends topics in linear algebra and operator theory for linear transformations on complex vector spaces to those on bicomplex Hilbert and Banach spaces. For example, Definition 3 for the first time defines a bicomplex vector space, its dimension, and its basis in terms of a corresponding vectorial idempotent representation, and the paper shows how an n by n bicomplex matrix's idempotent representation leads to its bicomplex Jordan form and a description of its bicomplex invariant subspace lattice diagram. Similarly, the paper rigorously defines for the first time "bicomplex Banach and Hilbert" spaces, and then it expands the theory of compact operators on complex Banach and Hilbert spaces to those on bicomplex Banach and Hilbert spaces. In these ways, the paper shows that complex linear algebra and operator theory are not necessarily built upon the broadest and most natural set of scalars to study. Instead, when using the idempotent representation, such results surprisingly generalize in a straightforward way to the higher-dimensional case of bicomplex values., Comment: 12 pages, 2 figures