1、正对角
>> v = [1 2 3 4 5 6 7 8 9]
v =
1 2 3 4 5 6 7 8 9
>> diag(v)
ans =
1 0 0 0 0 0 0 0 0
0 2 0 0 0 0 0 0 0
0 0 3 0 0 0 0 0 0
0 0 0 4 0 0 0 0 0
0 0 0 0 5 0 0 0 0
0 0 0 0 0 6 0 0 0
0 0 0 0 0 0 7 0 0
0 0 0 0 0 0 0 8 0
0 0 0 0 0 0 0 0 9
2、上对角
>> v = [1 2 3 4 5 6 7 8 9]
v =
1 2 3 4 5 6 7 8 9
>> diag(v,1)
ans =
0 1 0 0 0 0 0 0 0 0
0 0 2 0 0 0 0 0 0 0
0 0 0 3 0 0 0 0 0 0
0 0 0 0 4 0 0 0 0 0
0 0 0 0 0 5 0 0 0 0
0 0 0 0 0 0 6 0 0 0
0 0 0 0 0 0 0 7 0 0
0 0 0 0 0 0 0 0 8 0
0 0 0 0 0 0 0 0 0 9
0 0 0 0 0 0 0 0 0 0
3、下对角
>> v = [1 2 3 4 5 6 7 8 9]
v =
1 2 3 4 5 6 7 8 9
>> diag(v,-1)