matrixC

int element = 1;
            int columns = 0;
            for (int i = matrix.GetLength(0) - 1; i >= 0; i--)
            {
                for (int j = 0; j <= columns; j++)
                {
                    if (i == (matrix.GetLength(0) - 1))
                    {
                        matrix[i, j] = element;
                        element++;
                    }
                    else
                    {
                        matrix[i + j, j] = element;
                        element++;
                    }
                }
                columns++;
            }
            columns = matrix.GetLength(1) - 1;
            for (int i = 1; i <= matrix.GetLength(0); i++)
            {
                for (int j = 0; j < columns; j++)
                {
                    matrix[j, i + j] = element;
                    element++;
                }
                columns--;
            }