René Chrétien had noticed the 15x15 composite (4) magic square and showed me it is possible to use the method to construct magic squares of even orders as well.
Construct the 12x12 magic square by using 4 proportional 6x6 magic squares. The squares are proportional because all 4 magic 6x6 squares have the same magic sum of (1/2 x 870 = ) 435. We use the method with reflecting grids (6x6) to produce the magic 6x6 squares. As row coordinates don't use 0 up to 5 but use 0 up to (4x6 -/- 1 = ) 23 instead. Take care that the sum of the row coordinates in each 6x6 square is the same (0+7+8+15+16+23 = 1+6+9+14+17+22 = 2+5+10+13+18+21 = 3+4+11+12+19+20 = 69) to get proportional squares.
1x row coordinate +24x column coordinate + 1 = 6x6 magic square
0 | 7 | 15 | 8 | 16 | 23 | 0 | 5 | 0 | 5 | 5 | 0 | 1 | 128 | 16 | 129 | 137 | 24 | ||
23 | 7 | 8 | 15 | 16 | 0 | 1 | 1 | 4 | 4 | 1 | 4 | 48 | 32 | 105 | 112 | 41 | 97 | ||
0 | 16 | 8 | 15 | 7 | 23 | 3 | 2 | 2 | 2 | 3 | 3 | 73 | 65 | 57 | 64 | 80 | 96 | ||
23 | 16 | 8 | 15 | 7 | 0 | 2 | 3 | 3 | 3 | 2 | 2 | 72 | 89 | 81 | 88 | 56 | 49 | ||
23 | 7 | 15 | 8 | 16 | 0 | 4 | 4 | 1 | 1 | 4 | 1 | 120 | 104 | 40 | 33 | 113 | 25 | ||
0 | 16 | 15 | 8 | 7 | 23 | 5 | 0 | 5 | 0 | 0 | 5 | 121 | 17 | 136 | 9 | 8 | 144 | ||
1 | 6 | 14 | 9 | 17 | 22 | 0 | 5 | 0 | 5 | 5 | 0 | 2 | 127 | 15 | 130 | 138 | 23 | ||
22 | 6 | 9 | 14 | 17 | 1 | 1 | 1 | 4 | 4 | 1 | 4 | 47 | 31 | 106 | 111 | 42 | 98 | ||
1 | 17 | 9 | 14 | 6 | 22 | 3 | 2 | 2 | 2 | 3 | 3 | 74 | 66 | 58 | 63 | 79 | 95 | ||
22 | 17 | 9 | 14 | 6 | 1 | 2 | 3 | 3 | 3 | 2 | 2 | 71 | 90 | 82 | 87 | 55 | 50 | ||
22 | 6 | 14 | 9 | 17 | 1 | 4 | 4 | 1 | 1 | 4 | 1 | 119 | 103 | 39 | 34 | 114 | 26 | ||
1 | 17 | 14 | 9 | 6 | 22 | 5 | 0 | 5 | 0 | 0 | 5 | 122 | 18 | 135 | 10 | 7 | 143 | ||
2 | 5 | 13 | 10 | 18 | 21 | 0 | 5 | 0 | 5 | 5 | 0 | 3 | 126 | 14 | 131 | 139 | 22 | ||
21 | 5 | 10 | 13 | 18 | 2 | 1 | 1 | 4 | 4 | 1 | 4 | 46 | 30 | 107 | 110 | 43 | 99 | ||
2 | 18 | 10 | 13 | 5 | 21 | 3 | 2 | 2 | 2 | 3 | 3 | 75 | 67 | 59 | 62 | 78 | 94 | ||
21 | 18 | 10 | 13 | 5 | 2 | 2 | 3 | 3 | 3 | 2 | 2 | 70 | 91 | 83 | 86 | 54 | 51 | ||
21 | 5 | 13 | 10 | 18 | 2 | 4 | 4 | 1 | 1 | 4 | 1 | 118 | 102 | 38 | 35 | 115 | 27 | ||
2 | 18 | 13 | 10 | 5 | 21 | 5 | 0 | 5 | 0 | 0 | 5 | 123 | 19 | 134 | 11 | 6 | 142 | ||
3 | 4 | 12 | 11 | 19 | 20 | 0 | 5 | 0 | 5 | 5 | 0 | 4 | 125 | 13 | 132 | 140 | 21 | ||
20 | 4 | 11 | 12 | 19 | 3 | 1 | 1 | 4 | 4 | 1 | 4 | 45 | 29 | 108 | 109 | 44 | 100 | ||
3 | 19 | 11 | 12 | 4 | 20 | 3 | 2 | 2 | 2 | 3 | 3 | 76 | 68 | 60 | 61 | 77 | 93 | ||
20 | 19 | 11 | 12 | 4 | 3 | 2 | 3 | 3 | 3 | 2 | 2 | 69 | 92 | 84 | 85 | 53 | 52 | ||
20 | 4 | 12 | 11 | 19 | 3 | 4 | 4 | 1 | 1 | 4 | 1 | 117 | 101 | 37 | 36 | 116 | 28 | ||
3 | 19 | 12 | 11 | 4 | 20 | 5 | 0 | 5 | 0 | 0 | 5 | 124 | 20 | 133 | 12 | 5 | 141 |
Put the 4 magic 6x6 squares together.
12x12 magic square
1 | 128 | 16 | 129 | 137 | 24 | 2 | 127 | 15 | 130 | 138 | 23 |
48 | 32 | 105 | 112 | 41 | 97 | 47 | 31 | 106 | 111 | 42 | 98 |
73 | 65 | 57 | 64 | 80 | 96 | 74 | 66 | 58 | 63 | 79 | 95 |
72 | 89 | 81 | 88 | 56 | 49 | 71 | 90 | 82 | 87 | 55 | 50 |
120 | 104 | 40 | 33 | 113 | 25 | 119 | 103 | 39 | 34 | 114 | 26 |
121 | 17 | 136 | 9 | 8 | 144 | 122 | 18 | 135 | 10 | 7 | 143 |
3 | 126 | 14 | 131 | 139 | 22 | 4 | 125 | 13 | 132 | 140 | 21 |
46 | 30 | 107 | 110 | 43 | 99 | 45 | 29 | 108 | 109 | 44 | 100 |
75 | 67 | 59 | 62 | 78 | 94 | 76 | 68 | 60 | 61 | 77 | 93 |
70 | 91 | 83 | 86 | 54 | 51 | 69 | 92 | 84 | 85 | 53 | 52 |
118 | 102 | 38 | 35 | 115 | 27 | 117 | 101 | 37 | 36 | 116 | 28 |
123 | 19 | 134 | 11 | 6 | 142 | 124 | 20 | 133 | 12 | 5 | 141 |
Each 1/2 row/column/diagonal gives 1/2 of the magic sum and the 12x12 magic square is 6x6 compact.
Look at the tight sequence of the digits if you go from sub-square to sub-square forwards and backwards.
I have used composite method, proportional (1) to construct
8x8, 9x9, 12x12a, 12x12b, 15x15a, 15x15b, 16x16a, 16x16b, 18x18, 20x20a, 20x20b, 21x21a, 21x21b, 24x24a, 24x24b, 24x24c, 27x27a, 27x27b, 28x28a, 28x28b, 30x30a, 30x30b,32x32a, 32x32b and 32x32c