Inverse eigenproblems and approximation problems for the generalized reflexive and antireflexive matrices with respect to a pair of generalized reflection matrices

A matrix $P$ is said to be a nontrivial generalized reflection matrix over the real quaternion algebra $\mathbb{H}$ if $P^{\ast }=P\neq I$ and $P^{2}=I$ where $\ast$ means conjugate and transpose. We say that $A\in\mathbb{H}^{n\times n}$ is generalized reflexive (or generalized antireflexive) with respect to the matrix pair $(P,Q)$ if $A=PAQ$ $($or $A=-PAQ)$ where $P$ and $Q$ are two nontrivial generalized reflection matrices of demension $n$. Let ${\large \varphi}$ be one of the following subsets of $\mathbb{H}^{n\times n}$ : (i) generalized reflexive matrix; (ii)reflexive matrix; (iii) generalized antireflexive matrix; (iiii) antireflexive matrix. Let $Z\in\mathbb{H}^{n\times m}$ with rank$\left( Z\right) =m$ and $\Lambda=$ diag$\left( \lambda_{1},...,\lambda_{m}\right) .$ The inverse eigenproblem is to find a\ matrix $A$ such that the set ${\large \varphi }\left( Z,\Lambda\right) =\left\{ A\in{\large \varphi}\text{ }|\text{ }AZ=Z\Lambda\right\}$ nonempty and find the general expression of $A.$\newline In this paper, we investigate the inverse eigenproblem ${\large \varphi}\left( Z,\Lambda\right)$. Moreover, the approximation problem: $\underset{A\in{\large \varphi}}{\min\left\Vert A-E\right\Vert _{F}}$ is studied, where $E$ is a given matrix over $\mathbb{H}$\ and $\parallel \cdot\parallel_{F}$ is the Frobenius norm.