Frobenius Norm of a given matrix in Java

In this tutorial, I will show how to calculate the Frobenius Norm of a given matrix in Java. It is very basic and just involves a beginner level knowledge of how matrices work in programming. Let us get started.

Calculating the Frobenius Norm of a matrix in Java

I will first explain what is the Frobenius norm of a matrix. It is the square root of the sum of squares of each element in our matrix. I will show an example to make it more clear:

Matrix:

A = 1  2  3

    4  5  6

    7  8  9

Sum of squares = 285

Frobenius Norm = Square root of Sum of squares

               = √285 = 16.88

I will be using the OOPs concepts of Java to implement my approach to solve this problem. There are two functions in my class: calculate() and main() function.

calculate() function takes 3 user inputs passed as parameters in function calling in main() function. The three inputs will be the number of rows and columns of the matrix. Then a 2-D array will be having the elements of the matrix. Using a nested loop, I have calculated the sum of the square of each element. I have used the Math.sqrt() pre-defined function to calculate the square root of the sum we obtained. Note here that I have made my function static. I have done this because we need to pass an array to the function as a parameter. We cannot do this to a non-static method.

In the main() function, I have made an object of the Scanner class. After that, I have taken user input of the dimensions of the matrix. Following this, I have entered the elements of the matrix. I have made an object of our class and called our calculate() function by passing the parameters.

I have shown my code below:

import java.util.*;
public class Frobenius_Norm 
{
    static void calculate(int a[][], int m, int n)
    {
        int i,j;
        double sumofsquares = 0.0;
        double result;

        //Printing the matrix
        for(i=0;i<m;i++)
        {
            for(j=0;j<n;j++)
            {
                System.out.print(a[i][j] + " ");
            }
            System.out.println();
        }

        //Calculating sum of squares of each number
        for(i=0;i<m;i++)
        {
            for(j=0;j<n;j++)
            {
                sumofsquares = sumofsquares + a[i][j]*a[i][j];
            }
        }

        //Taking square root to get final result
        result = Math.sqrt(sumofsquares);

        System.out.println("Sum of Squares of all elements: " + sumofsquares);
        System.out.println("Frobenius Norm:                 " + result);
    }
    
    public static void main(String[] args)
    {
        Scanner ob = new Scanner(System.in);
        System.out.println("Enter no. of rows for matrix");
        int a = ob.nextInt();
        System.out.println("Enter no. of columns for matrix");
        int b = ob.nextInt();
        int A[][] = new int[a][b];
        System.out.println("Enter matrix");
        for(int i=0;i<a;i++)
        {
            for(int j=0;j<b;j++)
            {
                A[i][j] = ob.nextInt();       
            }
        }

        System.out.println("The matrix is: ");

        Frobenius_Norm fn = new Frobenius_Norm();

        fn.calculate(A, a, b);

    } 
}

Input:

I have entered the number of rows and number of columns. Once the dimensions are set, I input the elements of the matrix.

Output:

Enter no. of rows for matrix
3
Enter no. of columns for matrix
3
The matrix is:
1 2 3
4 5 6
7 8 9
Sum of Squares of all elements:    285.0
Frobenius Norm:                    16.881943016134134

Also read: Find whether an array is subset of another array in Java