矩阵的逆是什么
逆矩阵(inverse matrix),又称反矩阵。在线性代数中,给定一个n 阶方阵ReferenceError: katex is not defined,若存在一n 阶方阵ReferenceError: katex is not defined ,使得ReferenceError: katex is not defined,其中ReferenceError: katex is not defined为n 阶单位矩阵,则称ReferenceError: katex is not defined 是可逆的,且ReferenceError: katex is not defined 是ReferenceError: katex is not defined的逆矩阵,记作ReferenceError: katex is not defined。
只有方阵(n×n 的矩阵)才可能有逆矩阵。若方阵ReferenceError: katex is not defined的逆矩阵存在,则称ReferenceError: katex is not defined为非奇异方阵或可逆方阵。
与行列式类似,逆矩阵一般用于求解联立方程组。
矩阵的逆怎么求
矩阵的逆矩阵怎么求,我们来看下如何计算逆矩阵,有两种方法:
伴随矩阵法
如果矩阵ReferenceError: katex is not defined可逆,则ReferenceError: katex is not defined其中ReferenceError: katex is not defined是ReferenceError: katex is not defined的伴随矩阵。
注意:ReferenceError: katex is not defined中元素的排列特点是ReferenceError: katex is not defined的第ReferenceError: katex is not defined列元素是ReferenceError: katex is not defined的第ReferenceError: katex is not defined行元素的代数余子式。要求得ReferenceError: katex is not defined即为求解ReferenceError: katex is not defined的余因子矩阵的转置矩阵。
初等变换法
如果矩阵ReferenceError: katex is not defined和ReferenceError: katex is not defined互逆,则ReferenceError: katex is not defined。由条件ReferenceError: katex is not defined以及矩阵乘法的定义可知,矩阵ReferenceError: katex is not defined和ReferenceError: katex is not defined都是方阵。再由条件ReferenceError: katex is not defined以及定理“两个矩阵的乘积的行列式等于这两个矩阵的行列式的乘积”可知,这两个矩阵的行列式都不为0。也就是说,这两个矩阵的秩等于它们的级数(或称为阶,也就是说,A与B都是ReferenceError: katex is not defined方阵,且ReferenceError: katex is not defined.换而言之, ReferenceError: katex is not defined与ReferenceError: katex is not defined均为满秩矩阵)。换句话说,这两个矩阵可以只经由初等行变换,或者只经由初等列变换,变为单位矩阵。
因为对矩阵ReferenceError: katex is not defined施以初等行变换(初等列变换)就相当于在ReferenceError: katex is not defined的左边(右边)乘以相应的初等矩阵,所以我们可以同时对ReferenceError: katex is not defined和ReferenceError: katex is not defined施以相同的初等行变换(初等列变换)。这样,当矩阵ReferenceError: katex is not defined被变为ReferenceError: katex is not defined时,ReferenceError: katex is not defined就被变为ReferenceError: katex is not defined的逆阵ReferenceError: katex is not defined。
矩阵的逆的性质
- $$\left (A^{-1} \right )^{-1}=A$$
- $$(\lambda A)^{-1}=\frac{1}{\lambda}\times A^{-1}$$
- $$(AB)^{-1}=B^{-1}A^{-1}$$
- $$\left (A^\mathrm{T} \right )^{-1}=\left (A^{-1} \right )^{\mathrm{T}}$$($$A^{\mathrm{T}}$$为A的转置)
- $$\det(A^{-1})=\frac{1}{\det(A)}$$(det为行列式)