1) dot multiplication is the operation of finding the product of vectors, also called inner product, and the result is a real number.

When I entered the university, I studied the outer product, and the result was still a vector.

(2) When "A/B" is divisible by a matrix without points, the problem can be described as: Given two vectors A and B, find a constant X so that A = X * B. ..

For example: [2 4]/[ 1 2]=2. When each set of corresponding elements in two vectors has a fixed ratio, the answer is simple, which is equal to the ratio of any set of corresponding elements. However, if the ratio of corresponding elements in two vectors is not equal, for example, [2 5]/[12] =?

In many cases, we have measured two sets of vector data, and we know that they meet a fixed multiple relationship, and the specific ratio needs us to find. However, due to various reasons, there are measurement errors in the data, and the ratio of each group of data is different, so we can only choose an appropriate ratio to make one vector equal to the other vector as much as possible after multiplying this ratio (the corresponding elements in the two vectors are equal as much as possible, but not all). Generally, it is expressed by the least square sum of errors. Take [2 5]/[ 1 2] as an example to find a constant.