matlab 怎么输入n阶矩阵（n是不确定的）

用循环语句赋值最容易明白.
n=5;
a=2*eye(n);
for i=1:n-1
a(i+1,i)=-1;
a(i,i+1)=-1;
end
a(n,1)=-1;
a(1,n)=-1;
a
[v,d]=eig(a)
a =
2 -1 0 0 -1
-1 2 -1 0 0
0 -1 2 -1 0
0 0 -1 2 -1
-1 0 0 -1 2
v =
0.4472 -0.2165 0.5942 -0.4640 0.4298
0.4472 0.4982 0.3896 0.1228 -0.6204
0.4472 0.5245 -0.3535 0.2653 0.5741
0.4472 -0.1741 -0.6080 -0.5521 -0.3085
0.4472 -0.6321 -0.0223 0.6280 -0.0749
d =
-0.0000 0 0 0 0
0 1.3820 0 0 0
0 0 1.3820 0 0
0 0 0 3.6180 0
0 0 0 0 3.6180