Adding Matrices in C#?

Question

I'm trying to add two matrices together in C# using some simple for loops. I store the results in a data grid view. However, the last cell does not seem to add. I've been looking at this code for a while now and can't seem to figure it out. Did I do something wrong?

    // Adds two matrices together using arrays.
    private void menuItemAdd_Click(object sender, EventArgs e)
    {
        // Create two 2-D arrays
        int[,] matrixOne = new int[dgvMatrixOne.RowCount, dgvMatrixOne.ColumnCount];
        int[,] matrixTwo = new int[dgvMatrixTwo.RowCount, dgvMatrixTwo.ColumnCount];

        // The rows of the total matrix match the rows of the first matrix.
        dgvMatrixTotal.RowCount = dgvMatrixOne.RowCount;

        // The columns of the total matrix match the columns of the first matrix.
        dgvMatrixTotal.ColumnCount = dgvMatrixOne.ColumnCount;

        // Fill matrix one with the data in the data grid matrix one.
        for (int i = 0; i < dgvMatrixOne.RowCount; i++)
        {
            for (int j = 0; j < dgvMatrixOne.ColumnCount; j++)
            {
                matrixOne[i, j] = Convert.ToInt32(dgvMatrixOne[i, j].Value);
            }
        }

        // Fill matrix two with the data in the data grid matrix two.
        for (int i = 0; i < dgvMatrixTwo.RowCount; i++)
        {
            for (int j = 0; j < dgvMatrixTwo.ColumnCount; j++)
            {
                matrixTwo[i, j] = Convert.ToInt32(dgvMatrixTwo[i, j].Value);
            }
        }

        // Set the total data grid to matrix one + matrix two.
        for (int i = 0; i < dgvMatrixOne.RowCount; i++)
        {
            for (int j = 0; j < dgvMatrixOne.ColumnCount; j++)
            {
                dgvMatrixTotal[i, j].Value = matrixOne[i, j] + matrixTwo[i, j];
            }
        }
    }

Answer 1

Are you sure that your matrix have exactly the same size, theses two lines are strange anyway because you take the row count from one matrix but the columncount from another.

dgvMatrixTotal.RowCount = dgvMatrixOne.RowCount;
dgvMatrixTotal.ColumnCount = dgvMatrixTwo.ColumnCount;

---

I believe that your error is that MSDN state that the Item property (used for array-like access with the [] operator) is :

public DataGridViewCell this [
    int columnIndex,
    int rowIndex
] { get; set; }

But you allways use it in the invert order (row before column).

Answer 2

In a language like C#, you've no real need to worry about this stuff. There are tried and tested class libraries that do that sort of thing for you, and importantly, they're optimised take advantage of your processors' SIMD instructions etc. If the language has operator overloading, you'll just need to do declare your matrices as objects, and add them together with a simple result = mat_a + mat_b.

Answer 3

I'm not really answering you question as to what is wrong with your code... But I know how your can fix it. Just skip making your own Matrix math and use a 3rd party implementation! Go ahead, be lazy. ;)

I recommend the open source project Math.NET's Iridium Package. It provides most of the matrix transformations you will ever need.