Detail about the magic square
http://en.wikipedia.org/wiki/Magic_square.

To design a matrix sqaure, consider a 3X3 matrix.

n = 3;

* Fill the matrix with 0 or X. Start from the middle of the
first row ( i = 0, j = n/2)
+--+--+--+
|X_|1_|X_|
|X_|X_|X_|
|X_|X_|X_|

*. From 1, Go up rt corner(no row, and last column)(-1, 2),
and come down. and fill the next number at (2, 2)

X 1 X
X X X
X X 2

*. From 2, go right up corner( No  column, 2nd row)(1, -1)
and if not any column, take a left and fill the next number
at (1, 0)

X 1 X
3 X X
X X 2

* From 3, go right up(0,1), It's already accupied, so come
down(2, 0) and fill the next number at (2,0)
X 1 X
3 X X
4 X 2.

* From node 4(2,0), up right up (1, 1), Its not accupied,
fill the next number at (1, 1)

X 1 X
3 5 X
4 X 2.

* From 5(1,1), Go right up(0,2) and its not accupied, fill
the next number at (0, 2)
X 1 6
3 5 X
4 X 2

* From x(0,2), go right up(No row, no column), so come down
from 6(1, 2), Its not accupied fill with the next number 7
at (1, 2)

X 1 6
3 5 7
4 X 2

* From 7(1, 2), Go up rt(1st row, no column), so take a left
and fill the unfilled node (0, 0)

8 1 6
3 5 7
4 X 2

* From 8(0,0), take up rt( No row, 1st column), come down
and fill the unfilled node at ( 2, 1)

           8 1 6  sum = 15
           3 5 7  sum = 15
           4 9 2  sum = 15

     sum   15 15 15

     Diagonal sum = 15

Fallow the same procedure for 5X5, 7X7 square.