请输入您要查询的字词:

 

单词 DeterminantAsAMultilinearMapping
释义

determinant as a multilinear mapping


Let 𝐌=(Mij) be an n×n matrix with entries in a fieldK. The matrix 𝐌 is really the same thing as a list of n columnvectorsMathworldPlanetmath of size n. Consequently, the determinantMathworldPlanetmath operationMathworldPlanetmath may beregarded as a mapping

det:Kn××Knn timesK

The determinant of a matrix 𝐌 is then defined to bedet(𝐌1,,𝐌n),where 𝐌jKn denotes the jth column of 𝐌.

Starting with the definition

det(𝐌1,,𝐌n)=πSnsgn(π)M1π1M2π2Mnπn(1)

the following properties are easily established:

  1. 1.

    the determinant is multilinear;

  2. 2.

    the determinant is anti-symmetric;

  3. 3.

    the determinant of the identity matrixMathworldPlanetmath is 1.

These three properties uniquely characterize the determinant, andindeed can — some would say should — be used as the definition ofthe determinant operation.

Let us prove this. We proceed by representing elements of Knas linear combinationsMathworldPlanetmath of

𝐞1=(1000),𝐞2=(0100),𝐞n=(0001),

the standard basis of Kn. Let 𝐌 be an n×n matrix.The jth column is represented as iMij𝐞i; whenceusing multilinearity

det(𝐌)=det(iMi1𝐞i,iMi2𝐞i,,iMin𝐞i)
=i1,,in=1nMi11Mi22Minndet(𝐞i1,𝐞i2,,𝐞in)

The anti-symmetry assumptionPlanetmathPlanetmath implies that the expressionsdet(𝐞i1,𝐞i2,,𝐞in) vanish if any two of theindices i1,,in coincide. If all n indices are distinct,

det(𝐞i1,𝐞i2,,𝐞in)=±det(𝐞1,,𝐞n),

the sign in the above expression beingdetermined by the number of transpositionsMathworldPlanetmath required to rearrangethe list (i1,,in) into the list (1,,n). The sign istherefore the parity of the permutationMathworldPlanetmath (i1,,in). Since wealso assume that

det(𝐞1,,𝐞n)=1,

we now recover the original definition(1).

随便看

 

数学辞典收录了18232条数学词条,基本涵盖了常用数学知识及数学英语单词词组的翻译及用法,是数学学习的有利工具。

 

Copyright © 2000-2023 Newdu.com.com All Rights Reserved
更新时间:2025/5/4 10:16:19