[Solved] Power method, eigenvalues.
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function l = ww(A,E)
n = length(A);
y = [];
x = [];
for i = 1:n % starting vector
x(i) = A(i,1);
end;
l = 0;
blad = E; % starting value of error
while blad>=E
for i = 1:n % A*x
y(i) = 0;
for j = 1:n
y(i) = y(i) + A(i,j)*x(j);
end;
end;
blad = l;
l = 0; % Rayleigh
m = 0;
for i = 1:n
l = l + x(i)*y(i);
m = m + x(i)*x(i);
end;
l = l/m; % eigenvalue
blad = abs(l - blad); % error
x = y;
end;
end
That's how I've tried to compute eigenvalues. It works for some matrices, but for:
A =
0 -0.3333 -0.3333
-0.3333 0 0.3333
0.6000 0.2000 0
it doesn't work. How can I fix that?
7 个评论
Walter Roberson
2011-5-12
What difference do you see between what you expect and what is output?
Matt Fig
2011-5-12
And what is the input E??
John D'Errico
2011-5-12
Wow. Looks just like Fortran code to me.
Andrew Newell
2011-5-13
Fortran 77; 90 has vector operations.
Kamil
2011-5-13
Lorenzo Amabili
2017-3-17
编辑：Lorenzo Amabili
2017-3-17
@Kamil
@Teja Muppirala
how do you set E initially? I am sorry in case this question is silly but I am still new to this field. Thank you!
karim hamza
2017-4-29
i have an error [not enough input argument]
采纳的回答
Teja Muppirala
2011-5-13
Simple power iteration only works when there is a single dominant eigenvalue. The matrix
A =[ 0 -0.3333 -0.3333
-0.3333 0 0.3333
0.6000 0.2000 0];
has 3 eigenvalues,
-0.3333
0.1667 + 0.3249i
0.1667 - 0.3249i
with absolute values:
0.3333
0.3651
0.3651
As you can see, the dominant eigenvalue is not unique. That is why your algorithm fails to converge.
One way to fix this is by using shifts (you can read all about it on Google).
But why not just use MATLAB's built in eigevnalue solver, EIG?
eig(A)
更多回答（3 个）
Andrew Newell
2011-5-12
While we wait for more information, here is a vectorized version of whatever your algorithm is doing:
function l = ww(A,E)
x = A(:,1);
l = 0;
blad = E; % starting value of error
while blad>=E
y = A*x;
blad = l;
l = x.*y; % Rayleigh
m = x.*x;
l = l/m; % eigenvalue
blad = abs(l - blad); % error
x = y;
end;
2 个评论
devalaraju venkata naga amulya
2019-7-24
when i run the above code there is an error of input values A and E(in line function) can u help it with me im sorry im very new to the matlab
Dhruv Bhavsar
2020-8-28
Try calling the function in the command prompt even if you get the above mentioned error.
If it works then copy the function at the bottom of a new script and write the codes to be implemented above the function defined.
I have attached my code file for your reference.
Akankshya
2024-2-13
0 个投票
function l = ww(A,E)
x = A(:,1);
l = 0;
blad = E; % starting value of error
while blad>=E
y = A*x;
blad = l;
l = x.*y; % Rayleigh
m = x.*x;
l = l/m; % eigenvalue
blad = abs(l - blad); % error
x = y;
end
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