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)

ans =

0 0 0 0 0 0 0 0 0 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