For a given matrix $ G \in \mathbb{R}^{l \times n} $, define a subspace $ \Omega $ by $ \Omega = \left\{ z \in \mathbb{R}^n \mid Gz = 0 \right\} $, and let $ \mathcal{H} = \left\{ K \in \mathbb{R}^{n \times n} \mid (x, Ky) = (Kx, y), \, x^\top Kx \ge 0, \, \forall x, y \in \Omega \right\} $. Thus, $ \mathcal{H} $ consists of all symmetric nonnegative definite matrices on the subspace $ \Omega $. In this paper, we investigate the existence of $ X\in \mathcal{H} $ satisfying the linear matrix equations $ AX = C, XB = D $, and $ AXB = D $. A necessary and sufficient condition for solvability and an explicit representation of the general solution are obtained. Finally, two numerical examples are provided to demonstrate the accuracy of the results.
Citation: Yinlan Chen, Qingyi Yang, Honglin Zou. Symmetric nonnegative definite solutions of certain linear matrix equations on a subspace[J]. AIMS Mathematics, 2026, 11(7): 21727-21742. doi: 10.3934/math.2026879
For a given matrix $ G \in \mathbb{R}^{l \times n} $, define a subspace $ \Omega $ by $ \Omega = \left\{ z \in \mathbb{R}^n \mid Gz = 0 \right\} $, and let $ \mathcal{H} = \left\{ K \in \mathbb{R}^{n \times n} \mid (x, Ky) = (Kx, y), \, x^\top Kx \ge 0, \, \forall x, y \in \Omega \right\} $. Thus, $ \mathcal{H} $ consists of all symmetric nonnegative definite matrices on the subspace $ \Omega $. In this paper, we investigate the existence of $ X\in \mathcal{H} $ satisfying the linear matrix equations $ AX = C, XB = D $, and $ AXB = D $. A necessary and sufficient condition for solvability and an explicit representation of the general solution are obtained. Finally, two numerical examples are provided to demonstrate the accuracy of the results.
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