运算符“dot"是什么意思(.) 意思? [英] What does operator "dot" (.) mean?

问题描述

给定代码:

 A = [1 2 3; 3 2 1]
 B = A.^2

输出:

B =

     1     4     9
     9     4     1

但是如果我这样做:B = A^2

输出是:

Error using  ^ 
Inputs must be a scalar and a square matrix.
To compute elementwise POWER, use POWER (.^) instead.

运算符 . 究竟做了什么?

What does the operator . do exactly ?

推荐答案

点本身不是运算符，.^ 是.

The dot itself is not an operator, .^ is.

.^ 是 pointwise¹(即元素方面)幂，因为 .* 是 逐点产品.

The .^ is a pointwise¹ (i.e. element-wise) power, as .* is the pointwise product.

.^阵列功率.A.^B 是元素 A(i,j) 到 B(i,j) 次幂的矩阵.A 和 B 的大小必须相同或兼容.

.^ Array power. A.^B is the matrix with elements A(i,j) to the B(i,j) power. The sizes of A and B must be the same or be compatible.

C.f.

• 数组与矩阵运算":https://mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html
• "Pointwise":http://en.wikipedia.org/wiki/Pointwise
• Element-Wise Operations":http://www.glue.umd.edu/afs/glue.umd.edu/system/info/olh/Numerical/Matlab_Matrix_Manipulation_Software/Matrix_Vector_Operations/elementwise

¹) 因此点.

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