Get non-zero eigenvalues and eigenvectors

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Fraser Price
Fraser Price 2018-11-25
回答： Christine Tobler 2018-11-26
I am simply looking to retrieve non-zero eigenvalues (and eigenvectors which correspond to them) from a matrix X. I am new to matlab and the eig() and eigs() functions don't seem to do what I want. How do I solve this?
  2 个评论
madhan ravi
madhan ravi 2018-11-25
upload your matrix and what's the desired result?
Fraser Price
Fraser Price 2018-11-25
编辑：Fraser Price 2018-11-25
For example for the matrix [1 2; 3 4] we have
X = [1 2; 3 4]
[V,L] = eig(X)
V =
-0.7071 -0.7071
0.7071 -0.7071
L =
1 0
0 0
But I only want L to contain non-zero eigenvalues and V to contain just the eigenvectors which correspond to them, i.e.
V =
-0.7071
0.7071
L =
1
I hope this is clear.

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回答（1 个）

Christine Tobler
Christine Tobler 2018-11-26
You could just remove the zero eigenvalues after computing them:
>> X = [1 1; 1 1]
X =
1 1
1 1
>> [V,l] = eig(X, 'vector')
V =
-0.7071 0.7071
0.7071 0.7071
l =
0
2
>> l == 0
ans =
2×1 logical array
1
0
>> V(:, l==0) = []
V =
0.7071
0.7071
>> l(l==0) = [];
l =
2
In practice, l==0 should probably be replaced by abs(l) < tol.

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