点积, 余弦定理,复共轭

点积:在数学中,数量积(dot product; scalar product,也称为点积)是接受在实数R上的两个向量并返回一个实数值标量二元运算。它是欧几里得空间的标准内积

http://baike.baidu.com/link?url=jVfGaAWPAfzatZsQuAztJKPJKJCGbzlMrwiFCNc6i-f4RfQatXL5JGz5IZmGJlQSJu0ReW3y89jmdQYqJkLlA8FxZsqFy-3TtKbNZdf5FngLOl0HM8jClkA5u6_GzKIMyQbVgU5jfLw1QokOGLtJjz9g566dNAhUTBGbV4m4FHi

两个向量a = [a1, a2,…, an]和b = [b1, b2,…, bn]的点积定义为:
a·b=a1b1+a2b2+……+anbn。
使用矩阵乘法并把(纵列)向量当作n×1 矩阵,点积还可以写为:
a·b=a*b^T,这里的b^T指示矩阵b的转置
A为  m x p 的矩阵,B为 p x n 的矩阵,那么称 m x n 的矩阵C为矩阵AB的乘积,记作 C = AB ,其中矩阵中的第 i 行第 j 列元素可以表示为:
例子:

 

余弦定理(The Law of Cosines)

http://baike.baidu.com/item/%E4%BD%99%E5%BC%A6%E5%AE%9A%E7%90%86#2_1

 

 

 

复共轭(complex conjugate):

https://en.wikipedia.org/wiki/Complex_conjugate

Geometric representation of z and its conjugate in the complex plane. The complex conjugate is found by reflecting z across the real axis.

In mathematics, the complex conjugate of a complex number is the number with equal real part and imaginary part equal in magnitude but opposite in sign.[1][2] For example, the complex conjugate of 3 + 4i is 3 − 4i.

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