Measuring Correlation

If we want to know a correlation between a boxer winning a match and using red pants, we can mathematically determine it based on past records of those conditions. There are four possible combinations of the conditions.

The boxer loses and he doesn’t use red pants (00)
The boxer loses and he uses red pants (01)
The boxer wins and he doesn’t use red pants (10)
The boxer wins and he uses red pants (11)

For example, we have the following past records.

Condition “00” is 23 times
Condition “01” is 10 times
Condition “10” is 45 times
Condition “11” is 9 times

Then, we can use the phi coefficient formula. The result of this formula is between -1 and 1. If the result is close to 0, it means the conditions have no correlation. If it is close to 1, it means the conditions are strongly correlated. Meanwhile, if it is negative, the correlation is strong but in the opposite way. The formula is as follows.

phi = (n11 x n00) – (n01 x n10) / sqrt(n1X x n0X x nX1 x nX0)

n1X represents the condition where the boxer wins, regardless of the color of his pants. While nX1 represents the condition where the red pants are used, regardless result of the match.

phi = (9 x 23) – (45 x 10) / sqrt( 54 x 33 x 19 x 68 )

phi = -243 / 1517

phi = -0.16

It shows that winning a match and the red pants have no correlation. What if there are more other conditions that may have a correlation to a win. For example, on a winning day, sometimes he drinks coffee before the match, talks to his girlfriend, or plays with his buddies. We can perform the formula separately for each condition and the main condition which is winning a match. For example, the result is as follows.

phi coffee = 0.8
phi girlfriend = -0.7
phi buddies = 0.05

It shows that drinking coffee has a strong correlation. Meanwhile talking to a girlfriend has negative value therefore the assumed condition should become “not talking to girlfriend”. We can also perform an additional phase which is combining the two potential conditions into a single condition so that it becomes “drinking coffee and not talking to girlfriend”. Then, we need to tally again all records where the boxer wins or loses while he both drinks coffee and doesn’t talk to his girlfriend or not.

Comments

Rangkaian Sensor Infrared dengan Photo Dioda

Keunggulan photodioda dibandingkan LDR adalah photodioda lebih tidak rentan terhadap noise karena hanya menerima sinar infrared, sedangkan LDR menerima seluruh cahaya yang ada termasuk infrared. Rangkaian yang akan kita gunakan adalah seperti gambar di bawah ini. Pada saat intensitas Infrared yang diterima Photodiode besar maka tahanan Photodiode menjadi kecil, sedangkan jika intensitas Infrared yang diterima Photodiode kecil maka tahanan yang dimiliki photodiode besar. Jika tahanan photodiode kecil maka tegangan V- akan kecil . Misal tahanan photodiode mengecil menjadi 10kOhm. Maka dengan teorema pembagi tegangan: V- = Rrx/(Rrx + R2) x Vcc V- = 10 / (10+10) x Vcc V- = (1/2) x 5 Volt V- = 2.5 Volt Sedangkan jika tahanan photodiode besar maka tegangan V- akan besar (mendekati nilai Vcc). Misal tahanan photodiode menjadi 150kOhm. Maka dengan teorema pembagi tegangan: V- = Rrx/(Rrx + R2) x Vcc V- = 150 / (150+10) x Vcc V- = (150/160) x 5

Setting Up Next.js Project With ESLint, Typescript, and AirBnB Configuration

If we initiate a Next.js project using the create-next-app tool, our project will be included with ESLint configuration that we can apply using yarn run lint . By default, the tool installs eslint-config-next and extends next/core-web-vitals in the ESLint configuration. The Next.js configuration has been integrated with linting rules for React and several other libraries and tools. yarn create next-app --typescript For additional configuration such as AirBnB, it is also possible. First, we need to install the peer dependencies of eslint-config-airbnb . We also add support for Typescript using eslint-config-airbnb-typescript . yarn add --dev eslint-config-airbnb eslint-plugin-import eslint-plugin-jsx-a11y eslint-plugin-react eslint-plugin-react-hooks yarn add --dev eslint-config-airbnb-typescript @typescript-eslint/eslint-plugin @typescript-eslint/parser After that, we can update the .eslintrc.json file for the new configuration. { "extends": [ "airb

Configuring Swap Memory on Ubuntu Using Ansible

If we maintain a Linux machine with a low memory capacity while we are required to run an application with high memory consumption, enabling swap memory is an option. Ansible can be utilized as a helper tool to automate the creation of swap memory. A swap file can be allocated in the available storage of the machine. The swap file then can be assigned as a swap memory. Firstly, we should prepare the inventory file. The following snippet is an example, you must provide your own configuration. [server] 192.168.1.2 [server:vars] ansible_user=root ansible_ssh_private_key_file=~/.ssh/id_rsa Secondly, we need to prepare the task file that contains not only the tasks but also some variables and connection information. For instance, we set /swapfile as the name of our swap file. We also set the swap memory size to 2GB and the swappiness level to 60. - hosts: server become: true vars: swap_vars: size: 2G swappiness: 60 For simplicity, we only check the exi

Managing MongoDB Records Using NestJS and Mongoose

NestJS is a framework for developing Node.js-based applications. It provides an additional abstraction layer on top of Express or other HTTP handlers and gives developers a stable foundation to build applications with structured procedures. Meanwhile, Mongoose is a schema modeling helper based on Node.js for MongoDB. There are several main steps to be performed for allowing our program to handle MongoDB records. First, we need to add the dependencies which are @nestjs/mongoose , mongoose , and @types/mongoose . Then, we need to define the connection configuration on the application module decorator. import { MongooseModule } from '@nestjs/mongoose'; @Module({ imports: [ MongooseModule.forRoot('mongodb://localhost:27017/mydb'), ], controllers: [AppController], providers: [AppService], }) Next, we create the schema definition using helpers provided by NestJS and Mongoose. The following snippet is an example with a declaration of index setting and an o

Enabling Single Webcam for Multiple Applications Access in Linux

A webcam can not be accessed by two or more applications simultaneously. The solution is you can duplicate the video stream and make it available for any application. In short, you create a virtual webcam. First, a webcam is commonly detected on /dev/video* . Before you go through the steps to duplicate video stream, you should check whether your webcam is working. You can try to capture video using VLC by this command. (For example, your webcam is on /dev/video0 ) $ vlc v4l2:///dev/video0 If it doesn't work, you can try to change its mode to 0777 and make sure there are no other applications accessing it. If it still doesn't work, you can buy a new webcam. Seriously. Don't buy a cheap and unknown-brand webcam. I have $5 webcam and it had wasted my time. $ apt-get install ffmpeg linux-generic v4l2loopback-dkms FFmpeg is the main application that will access your webcam and duplicate its video stream. V4L2loopback is needed to create multiple virtual capture devic

Configure Gitlab SMTP Setting

Gitlab CE or EE is shipped with the capability to send messages through SMTP service as the basic feature to send notifications or updates to the users. The configuration parameters are available in /etc/gitlab/gitlab.rb . Each SMTP service provider has a different configuration, therefore the Gitlab configuration parameters should be adjusted according to the requirements. Some examples have been provided by Gitlab here . This is an example if you use the Zoho service. gitlab_rails['smtp_enable'] = true gitlab_rails['smtp_address'] = "smtp.zoho.com" gitlab_rails['smtp_port'] = 587 gitlab_rails['smtp_authentication'] = "plain" gitlab_rails['smtp_enable_starttls_auto'] = true gitlab_rails['smtp_user_name'] = "gitlab@mydomain.com" gitlab_rails['smtp_password'] = "mypassword" gitlab_rails['smtp_domain'] = "smtp.zoho.com" This is another example of using Amazon SES w

LUKI NOTES

Search This Blog