vectors and spaces

1. intro:

   $\left[\begin{array}{lll}x & x & x\end{array}\right] \rightarrow$ element amount $(n)=n$ dimension

   $\mathbb{R}^n$ (e.g. n = 3 3 Dimension)

Model representation

To describe supervised learning,we establish notation for future use.

**$x^i$ **denote the input variables also called input features

**$y^i$ ** denote the output variables also called target variables that we are trying to predict.

A pair **($x^i, y^i$) **is called a training set.

Check for alphabet characters

P1533 Number Reverse

we just find the position of the character '.' and '/' and '%' and reverse the string before and after the character and omit the front zeros.

Usage of string.find()

Every time I use find function in C++ , I always search its usage after using it for so many times. So I decide to make a summary of some commonly used usages.

KMP

KMP is an algorithm that find the given pattern string in the pending string. Usually we would think of violent traversing the two strings using for loop. However the time complexity of this method is O(n)~O(mn). So the KMP can cut the times of loop.

Add Comments

Because of my first theme was so incomplete that I need to add many features myself. So I’ve looked for how to add comment system on the blog.

Change Blog Theme

Last time I‘ve talked about how to build your own blog, however, the original theme might not very beautiful to you. So this time I would write how to change your blog theme and others.

Inclusion Exclusion Principle

In combinatorics (combinatorial mathematics), the inclusion–exclusion principle is a counting technique which generalizes the familiar method of obtaining the number of elements in the union of two finite sets; – From Wikipedia

Prime factor of n