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In mathematics, the Smith normal form is a normal form that can be defined for any matrix (not necessarily square) with entries in a principal ideal domain (PID). The Smith normal form of a matrix is diagonal, and can be obtained from the original matrix by multiplying on the left and right by invertible square matrices. In particular, the integers are a PID, so one can always calculate the Smith normal form of an integer matrix. The Smith normal form is very useful for working with finitely generated modules over a PID, and in particular for deducing the structure of a quotient of a free module. ==Definition== Let ''A'' be a nonzero ''m''×''n'' matrix over a principal ideal domain ''R''. There exist invertible and -matrices ''S, T'' so that the product ''S A T'' is and the diagonal elements satisfy . This is the Smith normal form of the matrix ''A''. The elements are unique up to multiplication by a unit and are called the ''elementary divisors'', ''invariants'', or ''invariant factors''. They can be computed (up to multiplication by a unit) as : where (called ''i''-th ''determinant divisor'') equals the greatest common divisor of all minors of the matrix ''A''. 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「Smith normal form」の詳細全文を読む スポンサード リンク
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