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In mathematics, especially in linear algebra and matrix theory, the vectorization of a matrix is a linear transformation which converts the matrix into a column vector. Specifically, the vectorization of an ''m×n'' matrix ''A'', denoted by vec(''A''), is the ''mn'' × 1 column vector obtained by stacking the columns of the matrix ''A'' on top of one another: : Here represents the -th element of matrix and the superscript denotes the transpose. Vectorization expresses the isomorphism between these vector spaces (of matrices and vectors) in coordinates. For example, for the 2×2 matrix = , the vectorization is . ==Compatibility with Kronecker products== The vectorization is frequently used together with the Kronecker product to express matrix multiplication as a linear transformation on matrices. In particular, : for matrices ''A'', ''B'', and ''C'' of dimensions ''k×l'', ''l×m'', and ''m×n''. For example, if (the adjoint endomorphism of the Lie algebra gl(''n'',C) of all ''n×n'' matrices with complex entries), then , where is the ''n×n'' identity matrix. There are two other useful formulations: : : 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Vectorization (mathematics)」の詳細全文を読む スポンサード リンク
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