Matrix Determinant using Thread

[Lionel Rossi]

Hello to everyone,

I know that can be a stupid question, but i kindly ask you if you have a code for matrix multiplication with thread. My problem is that i need to generate n thread one for each cells of the matrix result.

This is the function that i had produce, it works but it doesn't do what i need

import java.util.Random;

public class MatrixTest {

//Creating the matrix
static int[][] mat = new int[3][3];
static int[][] mat2 = new int[3][3];
static int[][] result = new int[3][3];

public static void main(String [] args){

    //Creating the object of random class
    Random rand = new Random();


    //Filling first matrix with random values
    for (int i = 0; i < mat.length; i++) {
        for (int j = 0; j < mat[i].length; j++) {
            mat[i][j]=rand.nextInt(10);
        }
    }

    //Filling second matrix with random values
    for (int i = 0; i < mat2.length; i++) {
        for (int j = 0; j < mat2[i].length; j++) {
            mat2[i][j]=rand.nextInt(10);
        }
    }

    try{
        //Object of multiply Class
        Multiply multiply = new Multiply(3,3);

        //Threads
        MatrixMultiplier thread1 = new MatrixMultiplier(multiply);
        MatrixMultiplier thread2 = new MatrixMultiplier(multiply);
        MatrixMultiplier thread3 = new MatrixMultiplier(multiply);

        //Implementing threads
        Thread th1 = new Thread(thread1);
        Thread th2 = new Thread(thread2);
        Thread th3 = new Thread(thread3);

        //Starting threads
        th1.start();
        th2.start();
        th3.start();

        th1.join();
        th2.join();
        th3.join();

    }catch (Exception e) {
        e.printStackTrace();
    }

    //Printing the result
    System.out.println("\n\nResult:");
    for (int i = 0; i < result.length; i++) {
        for (int j = 0; j < result[i].length; j++) {
            System.out.print(result[i][j]+" ");
        }
        System.out.println();
    }
  }//End main

  }//End Class

   //Multiply Class
   class Multiply extends MatrixTest {

private int i;
private int j;
private int chance;

public Multiply(int i, int j){
    this.i=i;
    this.j=j;
    chance=0;
}

//Matrix Multiplication Function
public synchronized void multiplyMatrix(){

    int sum=0;
    int a=0;
    for(a=0;a<i;a++){
        sum=0;
        for(int b=0;b<j;b++){
            sum=sum+mat[chance][b]*mat2[b][a];
        }
        result[chance][a]=sum;
    }

    if(chance>=i)
        return;
    chance++;
}
}//End multiply class

//Thread Class
     class MatrixMultiplier implements Runnable {

private final Multiply mul;

public MatrixMultiplier(Multiply mul){
    this.mul=mul;
}

@Override
public void run() {
    mul.multiplyMatrix();
}
}

Anyone can help me please? I know that probably i ll have less fast of the program, but it is an exercise.

Thanks a lot for your cooperation and looking forward into your answer

best Regards

[Lionel Rossi]

Hi,

I've got a big problem for calculate matrix determinant using thread, is anyone have a code that can pass me for see in which way i can use thread for resolve this problem?

Best Regards

[Stephan van Hulst]

Hi Lionel, welcome to CodeRanch!

We don't hand out solutions here, but try to help you to get it on your own. I see you already made a topic about this that contains code, so I merged those two topics.

[Stephan van Hulst]

Can you explain to us what the problem is that you're experiencing? We can't help you if we don't know what's wrong.

[Lionel Rossi]

Stephan van Hulst wrote:Can you explain to us what the problem is that you're experiencing? We can't help you if we don't know what's wrong.

I've got two different problems:

1) I need to create a software for calculate the product of two matrix in which i need to use n thread one for each cells of the matrix result (For this problem i posted a code that calculate the product of matrix but not using n thread for each cells of the matrix result)
2) I need to create a software for calculate the determinant of the matrix using thread (I don't have any idea to how to create a software that do this)

[Campbell Ritchie]

Welcome to the Ranch (again)

Why do you say you need several threads?
What is the algorithm for calculating a matrix determinant?

[Lionel Rossi]

Campbell Ritchie wrote:Welcome to the Ranch (again)

Why do you say you need several threads?
What is the algorithm for calculating a matrix determinant?

Hi Campbell,

1) For the first point (Product of Matrix) it is the exercise that impose me to use n thread one for each cells i know that is not a good solution but i must do it
2) For calculate the matrix determinant i think that first i need to check the dimension of the matrix (If is 2x2 is simply). For matrix that have a dimension bigger than 2x2 i need to calculate minor complementary so for each step i need to eliminate one row and one column

[Stephan van Hulst]

Okay, so before you start working with threads, why don't you start by creating a Matrix class that models a single matrix, which contains a multiply(Matrix other) method that returns a new Matrix. You should also add a method determinant() that returns an int.

Try getting this code to work (hint, use unit tests!) and then show us your code, or show us where you get stranded with an explanation of the problem. Don't worry about threads yet!

[Lionel Rossi]

Stephan van Hulst wrote:Okay, so before you start working with threads, why don't you start by creating a Matrix class that models a single matrix, which contains a multiply(Matrix other) method that returns a new Matrix. You should also add a method determinant() that returns an int.

Try getting this code to work (hint, use unit tests!) and then show us your code, or show us where you get stranded with an explanation of the problem. Don't worry about threads yet!

I just finish the code of Matrix product

import java.util.Scanner;

class MatrixProduct extends Thread {
    
    private int[][] A;
    private int[][] B;
    private int[][] C;
    private int rig,col;
    private int dim;

    public MatrixProduct(int[][] A,int[][] B,int[][] C,int rig, int col,int dim_com)
    {
      this.A=A;    
      this.B=B;
      this.C=C;
      this.rig=rig;    
      this.col=col; 
      this.dim=dim_com;     
    }
    
    
    public void run()
    {
     for(int i=0;i<dim;i++){
      C[rig][col]+=A[rig][i]*B[i][col];        
     }      
     System.out.println("Thread "+rig+","+col+" complete.");        
    }          
}
public class MatrixMultiplication {
	public static void main(String[] args)
    {
        
     Scanner In=new    Scanner(System.in); 
     
      System.out.print("Row of Matrix A: ");     
      int rA=In.nextInt();
      System.out.print("Column of Matrix A: ");
      int cA=In.nextInt();
      System.out.print("Row of Matrix B: ");     
      int rB=In.nextInt();
      System.out.print("Column of Matrix B: ");
      int cB=In.nextInt();
      System.out.println();
      if(cA!=rB)
          {
              System.out.println("We can't do the matrix product!");
              System.exit(-1);
          }
           System.out.println("The matrix result from product will be "+rA+" x "+cB);
           System.out.println();
           int[][] A=new int[rA][cA];
           int[][] B=new int[rB][cB];
           int[][] C=new int[rA][cB];
           MatrixProduct[][] thrd= new MatrixProduct[rA][cB];
           
           System.out.println("Insert A:");
           System.out.println();
            for(int i=0;i<rA;i++)
             {
              for(int j=0;j<cA;j++)
              {
                  System.out.print(i+","+j+" = ");
                  A[i][j]=In.nextInt();
              }
             }        
             System.out.println();    
             System.out.println("Insert B:");
             System.out.println();
              for(int i=0;i<rB;i++)
              {
               for(int j=0;j<cB;j++)
                {
                System.out.print(i+","+j+" = ");
                B[i][j]=In.nextInt();
                }        
              }
              System.out.println();
           
            for(int i=0;i<rA;i++)
            {
             for(int j=0;j<cB;j++)
              {
                thrd[i][j]=new MatrixProduct(A,B,C,i,j,cA);
                thrd[i][j].start();
              }
            }
            
            for(int i=0;i<rA;i++)
            {
            	for(int j=0;j<cB;j++)
            	{
            		try{
            			thrd[i][j].join();
            		}
                catch(InterruptedException e){}
            	}
            }        
                
            System.out.println();
            System.out.println("Result");
            System.out.println();
            for(int i=0;i<rA;i++)
            {
            	for(int j=0;j<cB;j++)
            	{
            		System.out.print(C[i][j]+" ");
            	}    
            	System.out.println();            
            }       
    }      
}

I don't have no idea to how implement the method of determinant

[Stephan van Hulst]

Like I said, you will benefit from implementing a Matrix class with some simple operations on it:

final class Matrix {
  
  private int height, width;
  private final int[][] elements;
  
  Matrix(int height, int width) {
    if (height < 0 || width < 0)
      throw new IllegalArgumentException();
    
    this.height = height;
    this.width  = width;
    
    this.elements = new int[height][width];
  }
  
  Matrix(int[][] elements) {
    if (elements == null)
      throw new IllegalArgumentException();
    
    this.height = elements.length;
    this.width  = (height == 0) ? 0 : elements[0].length;
    
    this.elements = new int[height][];
    for (int row = 0; row < height; row++)
      this.elements[row] = Arrays.copyOf(elements[row], width);
  }
  
  Matrix(Matrix toCopy) {
    this((toCopy == null) ? null : toCopy.elements);
  }
  
  int height() {
    return this.height;
  }
  
  int width() {
    return this.width;
  }
  
  private void assertIndicesAreInBounds(int row, int col) {
    if (
      row < 0 || row >= height ||
      col < 0 || col >= width
    ) {
      throw new IndexOutOfBoundsException();
    }
  }
  
  int element(int row, int col) {
    assertIndicesAreInBounds(row, col);
    return elements[row][col];
  }
  
  void setElement(int row, int col, int element) {
    assertIndicesAreInBounds(row, col);
    elements[row][col] = element;
  }
  
  void swapRows(int row1, int row2) {
    // Swap the two rows.
  }
  
  void multiplyRow(int row, int k) {
    // Multiply the elements of the row by k.
  }
  
  void addRow(int fromRow, int toRow, int k) {
    // Add the from-row k times to the to-row.
  }
  
  void reduce() {
    // Use row operations to transform this matrix to row reduced echelon form.
  }

  int determinant() {
    // Use the reduced form to find the determinant.
  }
  
  Matrix product(Matrix other) {
    // Find the product of this matrix with the other.
  }
  
  @Override
  public boolean equals(Object o) {
    if (!(o instanceof Matrix))
      return false;
    
    Matrix other = (Matrix) o;
    
    return Arrays.deepEquals(this.elements, other.elements);
  }
  
  @Override
  public int hashCode() {
    return Arrays.deepHashCode(elements);
  }
  
  @Override
  public String toString() {
    int cellWidth = Arrays.stream(elements)
      .flatMapToInt(Arrays::stream)
      .mapToObj(Integer::toString)
      .mapToInt(String::length)
      .max()
      .orElse(0);
    
    StringBuilder cellBottom = new StringBuilder();
    for (int i = 0; i < cellWidth; i++)
      cellBottom.append('-');
    cellBottom.append('+');
    
    StringBuilder rowBottom = new StringBuilder("+");
    for (int i = 0; i < width; i++)
      rowBottom.append(cellBottom);
    rowBottom.append('\n');
    
    StringBuilder result = new StringBuilder(rowBottom);
    for (int row = 0; row < height; row++) {
      for (int col = 0; col < width; col++)
        result.append(String.format("|%" + cellWidth + "d", elements[row][col]));
      
      result.append("|\n").append(rowBottom);
    }
    
    return result.toString();
  }
}

[Lionel Rossi]

Thanks for your help! I understood what did you told to me

Maybe at the moment i'm looking only for write the correct methods that works without think about the correct way in which i need to write software but i've got exam in these days on Java and i must clear all doubt if i want pass. Then next week i ll start to write good code for the final test (I ll create a programm with all UML diagram).

Best Regards