Question

The goal in this assignment is to perform various matrix multiplications. Input matrices A and B are read from a file. Output matrices A*A, A*B, B*A and B*B are written to file.

-Ask the user to enter the input and output file names.

-Read the input data matrices A and B from the input file. (A sample input file is shown in Appendix A)

            -Read the number of rows n.

            -Read matrix A, which has n rows and n columns.

            -Read string “A”.(this data is not used)

            -Read matrix B, which has n rows and n columns.

            -Read string “B”. (this data is not used)

- Calculate matrices AA, AB, BA and BB, where

            -AA=A*A

            -AB=A*B

            -BA=B*A

            -BB=B*B

-Write the following to the output file (A sample output file is shown in Appendix B. Use type double for the matrix elements, and include one decimal place in the output of each number)

            -String “First matrix A”

            - line space

            -Matrix A, which has n rows and n columns (requires n lines)

            -line space

            -String “Second matrix B”

            - line space

            -Matrix B, which has n rows and n columns (requires n lines)

            -line space

            -String “Matrix multiplication A*A”

            - line space

            -Matrix AA, which has n rows and n columns (requires n lines)

            -line space

            -String “Matrix multiplication A*B”

            - line space

            -Matrix AB, which has n rows and n columns (requires n lines)

            -line space

            -String “Matrix multiplication B*A”

            - line space

            -Matrix BA, which has n rows and n columns (requires n lines)

            -line space

            -String “Matrix multiplication B*B”

            - line space

            -Matrix BB, which has n rows and n columns (requires n lines)

            -line space

Note: Read and write matrixes from files, and explain each steps.

the language is JAVA.

Thank you.

Answer 1

Answer to the above question is as follows-

Reading file contents can be done though the Scanner class object.

But we can't write to a file using Scanner.

For the purpose of writing to a file we use the Writer class object. Then at last we close the opened files.

The required JAVA code is as follows -

import java.io.*;
import java.util.*;

class test {
  
  
/*function to multiply two matrices and return their product matrix */
public static int[][] multiplyTwoMatrices( int A[][], int B[][], int n){
  
int mul[][] = new int [n][n];
for (int i = 0; i < n; i++)
{
for (int j = 0; j < n; j++)
{
mul[i][j] = 0;
for ( int k = 0; k < n; k++)
mul[i][j] += A[i][k] *
B[k][j];
}
}
  
return mul;
}

// main method with all the functionalities
   public static void main (String[] args)throws FileNotFoundException,IOException {
       // may throw a IOException or FileNotFoundException
      
       // Scanner class to take user input of input and output file
       Scanner sc = new Scanner(System.in);
      
       //take input file name
       System.out.println("Enter the input file name.");
       String input = sc.nextLine();
      
       //take output file name
       System.out.println("Enter the output file name.");
       String output = sc.nextLine();
      
       //Scanner class object to read a file contents
       Scanner scanner = new Scanner(new File(input));
      
       int n = scanner.nextInt(); // to store the size of matrix
int [][] a = new int [n][n]; // store array A
int [][] b = new int [n][n]; // to store array B

  
// read 2d array A from file
for(int i = 0; i<n; i++ )
{
for( int j =0; j < n; j++){
a[i][j] = scanner.nextInt();
}
}
//read string A ( not usable )
String A = scanner.next();
  
// read 2d array B from file
for(int i = 0; i<n; i++ )
{
for( int j =0; j < n; j++){
b[i][j] = scanner.nextInt();
}
}
//read string B ( not usable )
String B = scanner.next();
  
  
//creating matrices to store the resulting matrices
int [][] aa = new int [n][n];
int [][] ab = new int [n][n];
int [][] ba = new int [n][n];
int [][] bb = new int [n][n];

//calling function ( defined above)to find the product matrices and store them accordingly
aa = multiplyTwoMatrices( a, a , n );
ab = multiplyTwoMatrices( a, b, n );
ba = multiplyTwoMatrices( b, a , n );
bb = multiplyTwoMatrices( b , b, n );
  
  
//Writer class object to write to the output file
Writer wr = new FileWriter(output);
  
// write the matrix A to the file
wr.write("First matrix A\n");
for(int i = 0; i<n; i++ )
{
for( int j =0; j < n; j++){
wr.write(String.valueOf( a[i][j] )); // write int to file
wr.write(" ");
}
wr.write("\n"); //change line
}
  
// write the matrix B to the file
wr.write("\nSecond matrix B\n");
for(int i = 0; i<n; i++ )
{
for( int j =0; j < n; j++){
wr.write(String.valueOf( b[i][j] )); // write int to file
wr.write(" ");
}
wr.write("\n"); //change line
}


// write the matrix product A*A to the file
wr.write("\nMatrix multiplication A*A\n");
for(int i = 0; i<n; i++ )
{
for( int j =0; j < n; j++){
wr.write(String.valueOf( aa[i][j] )); // write int to file
wr.write(" ");
}
wr.write("\n"); //change line
}
  
// write the matrix product A*B to the file
wr.write("\nMatrix multiplication A*B\n");
for(int i = 0; i<n; i++ )
{
for( int j =0; j < n; j++){
wr.write(String.valueOf( ab[i][j] )); // write int to file
wr.write(" ");
}
wr.write("\n"); //change line
}

// write the matrix product B*A to the file
wr.write("\nMatrix multiplication B*A\n");
for(int i = 0; i<n; i++ )
{
for( int j =0; j < n; j++){
wr.write(String.valueOf( ba[i][j] )); // write int to file
wr.write(" ");
}
wr.write("\n"); //change line
}
  
// write the matrix product B*B to the file
wr.write("\nMatrix multiplication B*B\n");
for(int i = 0; i<n; i++ )
{
for( int j =0; j < n; j++){
wr.write(String.valueOf( bb[i][j] )); // write int to file
wr.write(" ");
}
wr.write("\n"); //change line
}

wr.flush(); //flush Writer class object
wr.close(); // close the file


   }
  
}

Screenshot of the executed code is as follows-

The Screenshot of tested output is as follows -

Screenshot of the input file is as follows-

Screenshot of the output file is as follows-

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