Get non-zero eigenvalues and eigenvectors

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?

[madhan ravi]

upload your matrix and what's the desired result?

[Fraser Price]

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.

Answer 1

[Christine Tobler]

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.