How to multiply matrices in JavaScript

by Janeth Kent Date: 30-04-2021 javascript coding functions webdev


It may seem strange to want to know how to multiply matrices in JavaScript. But we will see some examples where it is useful to know how to perform this operation and how useful it is when handling coordinates as matrices, which we will see in a following article.

But let's go step by step and the first thing to do is to create a matrix in JavaScript. We have to know that an array is an array where each of the positions is an array of elements, for example numbers. In this way we can initialize an array in JavaScript as follows:

m1 = [[1,2,3],[4,5,6]];  
m2 = [[7,8],[9,10],[11,12]];

In order to understand what the columns and rows of the matrix would be, we will take into account that the elements of the main array are the rows and each of the elements of the internal array will be the columns. In this way the two arrays that we have instantiated in these lines of code would correspond to the matrices:

Matrix 2x3  
|1   2    3|    
|4   5   6|    

Matrix 3x2  
|7    8|  
|9   10|  
|11  12|

If we want to know how many rows and columns the matrix has, we can calculate it in the following way:

fil_m1 = m1.length;  
col_m1 = m1[0].length;    
fil_m2 = m2.length;  
col_m2 = m2[0].length;

We can see that the rows are obtained through the .length property of the array and the columns by asking the first element of the matrix, again with the .length property of the array.

This is very important because in order to be able to multiply matrices, the columns of the first matrix must be the same as the columns of the second matrix. We will make this check in the following way:

if (col_m1 != fil_m2)    
throw "Matrices cannot be multiplied";

The next step is to create the matrix with the result. The matrix will have a size equal to as many rows as matrix 1 as columns of matrix 2. So we create the matrix for the result of the multiplication as follows:

let multiplication = new Array(fil_m1);  
for (x=0; x<multiplication.length;x++)      
multiplication[x] = new Array(col_m2).fill(0);

We see that we first create an array and then for each element of the array we create a new element. We rely on the .fill() method that allows us to fill the array with a number. In this case we are going to initialise it to 0.

The next step is to perform the multiplication. To do this we go through the result matrix and in each x,y position we assign the result of multiplying each element of the row of the first matrix with each of the columns of the second matrix.

The scheme would be as follows

multiply matrices

And the code that implements it would be:

for (x=0; x < multiplication.length; x++) {      
for (y=0; y < multiplication[x].length; y++) {   
    for (z=0; z<col_m1; z++) {              
               multiplication [x][y] = multiplication [x][y] + m1[x][z]*m2[z][y]; 
               }      
    }  
}

In this way we will have managed to perform the multiplication and the result will be stored in the multiplication matrix. This way we will have managed to multiply matrices in JavaScript.

 
by Janeth Kent Date: 30-04-2021 javascript coding functions webdev hits : 5709  
 
Janeth Kent

Janeth Kent

Licenciada en Bellas Artes y programadora por pasión. Cuando tengo un rato retoco fotos, edito vídeos y diseño cosas. El resto del tiempo escribo en MA-NO WEB DESIGN END DEVELOPMENT.

 
 
 

Related Posts

Difference between arrow and normal functions in JavaScript

In this tutorial we are going to see how arrow functions differ from normal JavaScript functions. We will also see when you should use one and when you should use…

JavaScript Arrow functions: What they are and how to use them

In this article we are going to see what they are and how to use JavaScript Arrow Functions, a new feature introduced with the ES6 standard (ECMAScript 6). What are Arrow…

How to insert an element into an array with JavaScript

In this brief tutorial you will learn how to insert one or more elements into an array with JavaScript. For this we will use the splice function. The splice function will not…

What is the difference between primitives types and objects in JavaScript?

In this short tutorial we are going to look at the differences between primitive types and objects in JavaScript. To start with, we're going to look at what primitive types…

How to get DOM elements with JavaScript

When you access any element of the DOM, it is usual to save it in a variable. This is something that at first might seem very simple, but if you…

How to reverse an array in JavaScript

In this tutorial we are going to see how you can change the order of the elements of an array so that they are inverted. You could use a loop…

How synchronize the scroll of two divs with JavaScript

In case you have two divs of different sizes you may sometimes want to scroll both at the same time but at different speeds depending on their size. For example,…

How to use the codePointAt method in JavaScript

The JavaScript codePointAt method has more or less the same function as the charCodeAt method, used to get the 16-bit Unicode representation of the character at a certain position in…

How to check if a value is a number in JavaScript

In this short tutorial we are going to look at the various methods that exist to find out if a value is a number in JavaScript.   1. Using the isNaN() function   One…

How to use the charCodeAt method in JavaScript

The charCodeAt method is accepted by strings in JavaScript, returning the 16-bit Unicode code of the character at the position we pass as a parameter to the method. The charCodeAt method…

How to use the charAt method in JavaScript

The charAt method is accepted by strings in JavaScript, returning the position of the character passed as a parameter within the string. If the string contains multiple occurrences of the character…

Strings in JavaScript: What they are and how to use them

In this tutorial we are going to explain what strings are and how they are used in JavaScript. The tutorial is intended for people who are learning to program in…

We use our own and third-party cookies to improve our services, compile statistical information and analyze your browsing habits. This allows us to personalize the content we offer and to show you advertisements related to your preferences. By clicking "Accept all" you agree to the storage of cookies on your device to improve website navigation, analyse traffic and assist our marketing activities. You can also select "System Cookies Only" to accept only the cookies required for the website to function, or you can select the cookies you wish to activate by clicking on "settings".

Accept All Only sistem cookies Configuration