Adding Matrices Method. Double Array. Java

Question

Your have to add matrices. This does not work, and I'm not sure how to fix it! The two matrices I have inputed are shown below.

When I output the code, I get the location in the RAM instead of the added matrices.

I'm not sure where it went wrong! I would appreciate HELP! Thank you! :D

public static double[][] add(double[][] a1, double [][] a2)
{  
    for (int r = 0; r<a1.length; r++)
    {
        for (int c = 0; c<a1[r].length; c++)
        {
            a1[r][c] = a1[r][c] + a2[r][c];
        }

    }
    return a1;
}

public static void main(String[] args)
{
    double [][] arr = {{1,3,4},
                               {2,0,1}};

    double [][] arr1 = {{0,0,2},
                                 {5,6,7}};

    System.out.println(Matrix.add(arr, arr1));
}

Hovercraft Full Of Eels · Accepted Answer · 2013-11-20 03:36:56Z

3

You're calling println on an array, and you're seeing the toString() returned by an array. Don't do this. Either use Arrays.deepToString(...) or else use a for loop to iterate through the array printing out the results.

for example in pseudocode,

double[][] result = Matrix.add(...);
for go through rows
  for go through columns
    println the array item in the result array at row, column index

edited Nov 20, 2013 at 3:36

answered Nov 20, 2013 at 3:31

Hovercraft Full Of Eels

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4 Comments

user2990722 Over a year ago

Arrays.toString doesn't work. It gives the location in the RAM for arr and arr1.

Ted Hopp Over a year ago

Arrays.toString won't work for a double-indexed array. It will return a concatenation of each component's toString() result, which won't be any better than what OP is printing now.

Hovercraft Full Of Eels Over a year ago

@user2990722: see edit. Also there's the deepToString(...) method.

Hovercraft Full Of Eels Over a year ago

@TedHopp: you are right, but Arrays.deepToString(...) will work.

Michael Yaworski · Accepted Answer · 2013-11-20 03:47:01Z

0

You're not printing it properly. Try this (tested and works):

public static double[][] add(double[][] a1, double [][] a2)
{  
    for (int r = 0; r<a1.length; r++)
    {
        for (int c = 0; c<a1[r].length; c++)
        {
            a1[r][c] = a1[r][c] + a2[r][c];
        }
    }
    return a1;
}

public static void main(String[] args) 
{
    double [][] arr1 = {{1,3,4},{2,0,1}};
    double [][] arr2 = {{0,0,2},{5,6,7}};
    double[][] sumMatrix = add(arr1,arr2);

    for (double r[] : sumMatrix)
    {
        for (double c : r)
            System.out.print(c + ", ");

        System.out.println("" + '\n');
    }
}

answered Nov 20, 2013 at 3:47

Michael Yaworski

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