MATLAB: Can I plot eigenvalues corresponding to certain eigenvectors

equationmatrixplot

Hello everyone!
I've got a matrix 4×4 with with some kind of functions as a matrix elements. I would like to plot eigenvalues corresponding to certain eigenvector, in my case (-1 0 0 1). My idea is something like that (part of the code):
[vec,val]=eig(matrix);
       for n=1:4
       c=vec(:,n);
           if c(1)+c(4)==0 && c(1)~=0 && c(4)~=0
             y=loglog(w,(val(n,n));
             hold on;
          end
      end
It seems that loop with element 'c=vec(:,n)' is not sufficient for the case, as Matlab draws only a few points (for sure too few). What I would like to get: first loop (n=1:4) takes each of eigenvector of the system, and then (second loop) draws only those eigenvalues, which corresponds to the statements given as in the code above. Any idea how to fix my code?
Any help appreciated!

Best Answer

Well first you have to remember that the eigenvectors doesn't necessarily exactly match your desired one, so you'll have to be prepared to save away that deviation too.
Perhaps something along:
[vec,val]=eig(matrix);
target_vec = [-1 0 0 1];
[mostParallel,idxBest] = max(abs(vec*target_vec'));
Lambda_mostParallel = val(idxBest,idxBest);
HTH
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