# QA Official

### Personal Summary of Dimension Reduction PCA Principle

https://qaofficial.com/post/2019/04/04/68771-personal-summary-of-dimension-reduction-pca-principle.html 2019-04-04
Overview PCA is a classical dimensionality reduction method. The basic PCA is a linear dimensionality reduction method and is essentially a linear coordinate transformation. There are two kinds of classical PCA objective optimization interpretation ideas: one is to maximize variance in a single dimension, and the other is to minimize the distance from the sample point to the hyperplane by using the idea of least square linear regression.

### Principal Component Analysis (PCA)-MATLAB Program and Detailed Explanation of Functions

https://qaofficial.com/post/2019/04/04/68797-principal-component-analysis-pca-matlab-program-and-detailed-explanation-of-functions.html 2019-04-04
Reference Source: http://www.cnblogs.com/Hand-Head/articles/5156435.html http://www.matlabsky.com/thread-11751-1-1.html matlab Help Documents Program Source Code Download Link: http://download.csdn.net/detail/ckzhb/9903051 contains three M files: drtool_pca: function encapsulation.Box drawings are not included.Pca _ test: example of MATLAB-PCA () function princmp _ test: example of MATLAB-princmp () function example shows: It uses 9 indicators to measure the quality of life in 329 cities in the United States: climate, housing, health, crime rate, transportation, education, art, entertainment and economy. For

### Several Common Encryption Methods and Codes

https://qaofficial.com/post/2019/04/04/68879-several-common-encryption-methods-and-codes.html 2019-04-04
import java.io.UnsupportedEncodingException; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.Scanner; import org.apache.commons.codec.binary.Hex;/** * 常見的几种加密方式 */public class Encrypt { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String next = sc.next(); //123 String md5str = string2MD5(next); //202CB962AC59075B964B07152D234B70 String sha1str = string2Sha1(next); //40bd001563085fc35165329ea1ff5c5ecbdbbeef String sha256str = String2SHA256(next); //a665a45920422f9d417e4867efdc4fb8a04a1f3fff1fa07e998e86f7f7a27ae3 String sha256Javastr = String2SHA256StrJava(next); //a665a45920422f9d417e4867efdc4fb8a04a1f3fff1fa07e998e86f7f7a27ae3 System.out.println("next"); System.out.println("md5str:"+md5str); System.out.println("sha1str:"+sha1str); System.out.println("sha256str:"+sha256str); System

### Simple Text Emotion Analysis in python

https://qaofficial.com/post/2019/04/04/68827-simple-text-emotion-analysis-in-python.html 2019-04-04
Brief Introduction to Emotional Analysis; Emotional analysis is to analyze whether a sentence is subjective or objective, and whether it expresses positive or negative emotions.Principles such as the following sentence: " The picture of this mobile phone is excellent and its operation is relatively smooth.But taking pictures is really terrible!The system is not good either. "(1) emotional words to analyze a sentence is positive or negative, the simplest and most

### Simple Understanding of MD5 Information message digest algorithms

https://qaofficial.com/post/2019/04/04/68882-simple-understanding-of-md5-information-message-digest-algorithms.html 2019-04-04

### Some Concepts of Entropy and Consistency of Maximum Likelihood and Cross Entropy

https://qaofficial.com/post/2019/04/04/68874-some-concepts-of-entropy-and-consistency-of-maximum-likelihood-and-cross-entropy.html 2019-04-04
Information Quantity of Random Events In order to describe the information content of a random event, self-information is defined. Self-information indicates the degree of uncertainty. There is no information when an event is certain to occur.The smaller the probability of an event, the greater the amount of information. The uncertainty brought by the unknown is the target to be described by the self-information. Self-information: i (x) = log _ i \ frac { 1 } { p (x) } notice: the amount of self-information here does not represent the size of the role of information.

### Spring-Several Scenarios of IOC Container Bean Instantiation

https://qaofficial.com/post/2019/04/04/113450-spring-several-scenarios-of-ioc-container-bean-instantiation.html 2019-04-04
Several Scenarios of Bean Instantiation 1. instantiation of Beandefinitionregistrypostprocessor: extension of standard BeanFactoryPostProcessor. BeanFactoryPostProcessor is used to further define the registered BeanDefinition. IoC container is essentially bean management.Therefore, BeanActionTypostProcessor itself is also a Bean. To further define BeanActionTypostProcessor's BeanDefinition, register through BeanDefinitionRegistryPostProcessor. BeanDefinitionRegistryPostProcessor and its subclasses are the most instantiated Beans of Ioc container.They implement class call refresh () method call invokebeanfactorypostprocessors (beanfactory) in configurableapplicationcontext (applicationcontext subinterface);Method is instantiated when