# How can I decompose this matrix into the linear or bilinear product of two matrices?

Given the $$(m_1 + m_2) \times (n_1 + n_2)$$ block matrix $$A = \begin{bmatrix}A_{11} & A_{12} \\ A_{21} & A_{22}\end{bmatrix}$$ where $$A_{11} \in \mathbb R^{m_1 \times n_1},A_{12} \in \mathbb R^{m_1 \times n_2},A_{21} \in \mathbb R^{m_2 \times n_1},$$ and $$A_{22} \in \mathbb R^{m_2 \times n_2}$$, and given the non-block $$2 \times 2$$ matrix $$B = \begin{bmatrix}b_{11} & b_{12} \\ b_{21} & b_{22}\end{bmatrix}$$ is it possible to decompose the following $$(m_1 + m_2) \times (n_1 + n_2)$$ block matrix $$C = \begin{bmatrix}b_{11}A_{11} & b_{12}A_{12} \\ b_{21}A_{21} & b_{22}A_{22}\end{bmatrix}$$ into some product (such as Hadamard, Kronecker, or other linear/bilinear product) of the matrices $$A$$ and $$B$$?

• This could be interpreted as an instance of the Khatri-Rao product Commented Mar 31, 2023 at 15:41
• @BenGrossmann just what I'm looking for. Thanks! Feel free to add an answer and for me to accept. Commented Mar 31, 2023 at 15:45

This could be interpreted as an instance of the Khatri-Rao product. In general, for any two matrices $$\mathbf A$$ and $$\mathbf B$$ partitioned into $$2 \times 2$$ block matrices, their Khatri-Rao product is given by $$\mathbf{A} \ast \mathbf{B} = \left[ \begin{array} {c | c} \mathbf{A}_{11} \otimes \mathbf{B}_{11} & \mathbf{A}_{12} \otimes \mathbf{B}_{12} \\ \hline \mathbf{A}_{21} \otimes \mathbf{B}_{21} & \mathbf{A}_{22} \otimes \mathbf{B}_{22} \end{array} \right] .$$
• Just to add to this, in my case, I can decompose my $C$ block matrix as $C = A * B$, where $A$ and $B$ are defined in my question. Commented Mar 31, 2023 at 16:44