CODEWITHSUNDEEP
javaarraysmatrix
Baldwin D.
Baldwin D.

Reputation: 110

Special diagonal matrix in Java

Does anyone know how to construct following matrix in Java?

matrix

I can see a transpose pattern but I might be on the wrong track with that. This is what I've got so far... don't laugh :-)

import java.io.*;

public class Diagonal
{
   public static void main(String[] args)throws IOException
   {
      InputStreamReader isr = new  InputStreamReader(System.in);
      BufferedReader in = new BufferedReader(isr);

      int dim;

      do
      {
      System.out.print("Dimension: ");
      dim = Integer.parseInt(in.readLine());
      }while(dim<=0);

      int[][] matrix = new int[dim][dim];

      for(int i=0;i<matrix.length;i++)
      {
         for(int j=0;j<matrix[i].length;j++)
         {
               matrix[i][j] = j+1;   
         }
      }

      //Transpose
      int transpose[][] = matrix;

      for(int i=0;i<dim;i++)
      {    
         for(int j=0;j<dim;j++)
         {
            transpose[j][i] = matrix[i][j];
         }
      }

      //print transpose
      for(int i=0;i<transpose.length;i++)
      {
         for(int j=0;j<transpose[i].length;j++)
         {
            System.out.print(transpose[i][j]);
         }
         System.out.println("");   
      }      
   }
}

I'm not sure but I think it is called a toeplitz matrix...

Grts.

Upvotes: 2

Views: 4624

Answers (3)

loknath
loknath

Reputation: 1372

public static void createMatrix(int no) {
    int front = 1, last = no, position = 0;
    for (int i = 0; i < no; i++) {
        for (int j = front; j > 0; j--) {
            System.out.print(j);
        }
        for (int j = 2; j <= last; j++) {
            System.out.print(j);
        }
        front++;
        last--;
    }
}

output:

This function return a array like below

1, 2, 3, 4, 5, 6, 7, 8
2, 1, 2, 3, 4, 5, 6, 7
3, 2, 1, 2, 3, 4, 5, 6
4, 3, 2, 1, 2, 3, 4, 5
5, 4, 3, 2, 1, 2, 3, 4
6, 5, 4, 3, 2, 1, 2, 3
7, 6, 5, 4, 3, 2, 1, 2
8, 7, 6, 5, 4, 3, 2, 1

Upvotes: 0

sabhiram
sabhiram

Reputation: 907

A Toeplitz matrix implies that all diagonals in a given matrix are constants. Your matrix is a special type of Toeplitz matrix which is transpose-able. M == MT. Check out Circulant Matrices as well...

Notice that you are trying to find a matrix, where all values correspond to the distance (if you will) between i and j. Hence something like this will work:

int[][] matrix = new int[dim][dim];

for(int i=0;i<matrix.length;i++)
{
    for(int j=0;j<matrix.length;j++)
    {
        // Figure out distance from i -> j
        matrix[i][j] = Math.abs(i - j) + 1;   
    }
}

Upvotes: 2

assylias
assylias

Reputation: 328629

Note that: m[i][j] = Math.abs(i - j) + 1. Once you have seen that, creating the matrix is fairly simple:

private static int[][] createMatrix(int n) {
  int[][] m = new int[n][n];
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      m[i][j] = Math.abs(i - j) + 1;
    }
  }
  return m;
}

And you can try it out:

public static void main(String[] args) {
  for (int[] row : createMatrix(8)) {
    System.out.println(Arrays.toString(row));
  }
}

prints:

[1, 2, 3, 4, 5, 6, 7, 8]
[2, 1, 2, 3, 4, 5, 6, 7]
[3, 2, 1, 2, 3, 4, 5, 6]
[4, 3, 2, 1, 2, 3, 4, 5]
[5, 4, 3, 2, 1, 2, 3, 4]
[6, 5, 4, 3, 2, 1, 2, 3]
[7, 6, 5, 4, 3, 2, 1, 2]
[8, 7, 6, 5, 4, 3, 2, 1]

Upvotes: 5

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