DEV Community: aram

What are the genetic algorithms?

aram — Mon, 17 Feb 2020 13:11:12 +0000

This is a short article that explains what are genetic algorithms in general

Introduction

One of the fields in programming world is Artificial Intelligence we as humans make very weird solutions to some weirder problems that we have in our modern society which add a little bit knowledge to our understanding, in this article we are gonna talk about a field or a branch in AI which is called genetic algorithms what are they? how do they work? in what kind of problems we use them?

in simplest terms genetic algorithms are to solve those kind of problems which have multiple solutions or have a very large search space that is just unfeasible to try solving it with traditional programming.

The Idea

Best way to deliver our idea is to make an example or make a story and we try to understand through it basically genetic algorithms are using the idea of evolution and the concept of natural selection if we take a population of animals in nature we may find strong individuals, weak ones, old ones...
what is important here what are the individuals who reproduce and make a new generation

Problem Example

Let's say you have a a hypothetical echo system where animals have a DNA consisted only of binary numbers and the length of DNA for every animal is 8bit(1 byte) long rather miserable animals 🤔 but assume that what our goal is to find an animal that have a DNA which is exactly like 11111111

in another way the problem is like this
in a binary string of length 8 find a string that have all bits set to 1

to start solving those kind of problems which we know the solution but we miss the path to reaching that solution or at least approximation of the solution is acceptable we use genetic algorithms

in our example what is the best way to find an animal which have a DNA of 1's ?

the answer is simple Guessing is our best choice we generate random DNA samples and evaluate each sample and we pick only ones that are more like our ideal animal, our animals have genomes consist of chromosomes which consist of DNA's so animals in our echo system have 1 chromosome which contains 1 DNA stripe with size of 1 byte.

we talked about picking animals that are similar to our ideal animal evaluation is based on something called a fitness value and fitness function
fitness value : is related to each individual(animal in our case)
fitness function: is the function that assigns and evaluates fitness value for each individual saying this animal is more like our ideal animal ex: because it's DNA contains 5 ones so we pick that over another animal.

The Steps

Steps for approaching the solution we use our ideal animal example

Generate initial population

We start by making a population(an array) of 22 animals(DNA strings) randomly(math.random 😁) we call this Generation1 or g1

Run fitness function on g1

We run fitness function on g1 and assign fitness value to each animal or DNA string

Pick best animals to reproduce

What our randomly generated animals would do reproduce of course but it's not up to them to pick we do that by picking ones that have highest fitness value or there are multiple ways to do that it's called
Selection phase in academic books

a. Roulette Wheel Selection(we talk about this)
b. Rank Selection
c. Steady State Selection
d. Tournament Selection
e. Elitism Selection

let's say we went with Roulette Wheel Selection what this does it will assign a portion of the wheel to each individual based on their calculated fitness value the higher the value the larger are they occupy on the wheel
then we spin the wheel and pick a spot randomly what we see is that animals with higher fitness value are most likely to get picked

mating season 🎉

our animals do their thing and produce offspring's this action is called Crossover in academic books before we produce Generation2 or g2 we have another action that is happening while our animals do Crossover its called Mutation just like natural beings our baby animals are subjected mutation in our case maybe in each 1,000 baby we will change DNA of 3 of them at random by 1 bit also randomly this may increase the chance of getting closer to our ideal animal after that we say that we generated second generation g2

Repeat

What we did to generate g2 from g1 we repeat that process many times till we get closer and closer to our solution but when to stop is also our decision we may say that if you find an animal that is 85% like our ideal animal we stop and pick this as a solution.

Key points

1- Very good at approximating solutions that are hard to program or expensive to calculate

2- For very complex problems they may require many generations to produce a good approximation

3- Genetic algorithms weak point is that when you have time bounded variables in your logic which means our data may change according to time

Actual example

This is a demo what if we wanted to approximate a cat picture

Final words

This was a humble explanation for a very interesting topic if you find any inconsistency or mistake please correct me thanks.

Send automated reports using Nodejs

aram — Tue, 01 Oct 2019 06:40:35 +0000

Introduction

In this article we will explain how you can send reports automatically and periodically using a NodeJs whether you embed the logic inside your application or you make it a separate script its up to the developer but separate script is recommended(we use this approach), before you start you should know what is NodeJs you can benefit from this A Quick Guide to Node.js in 2019

Requirements

Two packages is required for this tutorial

node-cron used for scheduling tasks
node-mailer used to send emails to some user list using some SMTP providers googles Gmail will be used for this purpose as it is free and easy to setup

Project setup

Start by creating new NodeJs project

create a folder & cd to the folder using command line something like exampleFolder
run npm init this will ask you couple of questions after you finish there will be a file called package.json alternatively if you don't want to answer questions type npm init -y this will answer yes for all question,
install node-cron type npm i node-cron --save in the console
install nodemailer type npm i nodemailer --save in the console

After the installation you should see a folder called node_modules and generated package.json should look something like this

     {
       "name": "exampleFolder",
       "version": "1.0.0",
       "description": "",
       "main": "index.js",
       "scripts": {
          "test": "echo \"Error: no test specified\" && exit 1"
        },
        "keywords": [],
        "author": "",
        "license": "ISC",
        "dependencies": {
           "node-cron": "^2.0.3",
           "nodemailer": "^6.3.0"
        }
    }

Let's start coding

We need an entry point for our application(script) start by creating a file called main.js and add "start": "node main.js" line to package.json under "scripts" property so it becomes like this

     {
       "name": "exampleFolder",
       "version": "1.0.0",
       "description": "",
       "main": "index.js",
       "scripts": {
          "test": "echo \"Error: no test specified\" && exit 1",
          "start": "node main.js"
        },
        "keywords": [],
        "author": "",
        "license": "ISC",
        "dependencies": {
           "node-cron": "^2.0.3",
           "nodemailer": "^6.3.0"
        }
    }

Add console.log("Hello world") inside main.js then in the console type npm start this should output Hello world to the console this is used to make sure our application runs

Configure nodemailer

We will start by configuring nodemailer follow these steps

create a file called reportSender.js
paste this script inside the file

        const nodemailer = require('nodemailer');
        const defaultMailingList = "example1@vultr.com,example2@vultr.com";
        const senderEmail = "sender.example@gmail.com";
        const senderPassword = "gmail_app_password"; // gmail app password
        module.exports = {
            sendMail: async (subject, text, to = defaultMailingList) => {
                try {
                const transporter = nodemailer.createTransport({
                    service: 'Gmail',
                    auth: {
                    user: senderEmail,
                    pass: senderPassword,
                    },
                });

                const message = {
                    from: `report sender <${senderEmail}>`,
                    to,
                    subject,
                    text: subject,
                    html: text,
                };

                transporter.sendMail(message, () => {});
                } catch (e) {
                // handle errors here
                }
            },
        };

Note that nodemailer provides handful of transports including custom ones

Values are hardcoded i would recommend using something like dotenv which loads .env file and creates environment variables based on the environment variable but for sake of simplicity we did that here,

What this file does is that it exports an object with key sendMail which is a function that configures node mailer and setup a generic method for sending our reports as we please for future uses you can add extra keys to main object for example you want the report to be sended via telegram by a bot you can add the logic in this file

you can get gmail app password following this link get app password

Test if node mailer can send emails for us

after you change these variables in a correct way [senderEmail,senderPassword,defaultMailingList]
open main.js and import sendMail from reportSender.js using this syntax const {sendMail} = require('./reportSender') note that no file extension is required when importing
make a call to sendMail function so it can send and email example sendMail("Hello world", "this is email body it can contain html also") if you didnt update defaultMailingList to contain your email you can pass the email after msg body

the complete body of our main.js is something like this


            const {sendMail} = require('./reportSender');

            console.log('sending email...')
            sendMail("Hello world", "this is email body it can contain html also")
            console.log('email sent ✓')

With this we can send emails to some specific emails as you can predict that you can somehow generate a string which contains a valid html and this html is generated using data from our database then you can send reports or even data to your mailing list
if you are wondering what is a good module for database connection i would recommend using kenxjs
the only thing remains is to automate sending reports(emails) with that comes node-cron module

Configure node-cron

Configuring node-cron is an easy task you tell it when do you want for some action to take place then you provide the action definition and whenever the call triggers it will call this action, ction is a function

for sake of this tutorial let's say i want to receive a report every 1 min
what you can do according to their documentation is something like this


        var cron = require('node-cron');
        cron.schedule('* * * * *', () => {
            console.log('running a task every minute');
        });

You can test this code just comment everything inside main.js then wait for 1 min and you should see running a task every minute output every 1 min on the console as you can see the callback is our action and its the place that we want to implement and generate our reports then send the emails (generated reports)

Combine our nodemailer and node-cron

As you can see by combining just two modules we could make an automated system that can send reports or even anything that we want periodically so lte's show our final main.js

        const {sendMail} = require('./reportSender');
        var cron = require('node-cron');
        let counter = 1;
        cron.schedule('* * * * *', () => {
            /* 
                generate your report here then send the report using 
                any reportSender logic that you implemnted email, telegram bot,...
            */
            sendMail(`hello world ${counter}`, "this is email body it can contain html also");
            counter++;
        });

Final words

The idea have alot of potential so you could get creative and make anything you want, the reason i recommended making this as a separate script is that it become another process on the CPU so simply terminate the process if you want to stop the service, in production you have your separate system this script works as an assistant and provides a nice simple feature it could be run using something like pm2 which is strongly recommend.