C..1 冪乗法

% eigen1.m --- power method
format long
a=[1 1 1;1 2 2;1 2 3]
eigen=eig(a)
x=ones(3,1);
maxiter=10;
r=zeros(maxiter,1);
for k=1:maxiter
    y=a*x;
    x=y/norm(y);
    r(k)=x'*(a*x);
end
r
error=r-max(eigen)
clf
semilogy(1:maxiter,abs(error))