MATLAB Central Newsreader - arrengment of eigenvalu and eigenvector

arrengment of eigenvalu and eigenvector

mustafa alheety — Tue, 01 Jan 2008 06:56:59 -0500

Dear all...
Hello...

happy new year frist. please i want to ask if that
possible in matlab to give my the eigenvalue and eigen
vector arrengement decreasing

Re: arrengment of eigenvalu and eigenvector

feras batah — Tue, 01 Jan 2008 07:08:50 -0500

Re: arrengment of eigenvalu and eigenvector

Roger Stafford — Tue, 01 Jan 2008 10:26:48 -0500

"feras batah" <ferashaker2001@yahoo.com> wrote in message <flcou2$rsg
$1@fred.mathworks.com>...
> "mustafa alheety" <alheety@yahoo.com> wrote in message
> <flco7r$ieu$1@fred.mathworks.com>...
> >
> > happy new year frist. please i want to ask if that
> > possible in matlab to give my the eigenvalue and eigen
> > vector arrengement decreasing
>
> Hello Mustafa
> also i need this solve and more information for this
> problem in mat. porgram
> thanks happy new year
------
The trouble is that eigenvalues can very easily be complex-valued, and then
how would they be arranged in decreasing order? That is probably why
MathWorks' eig function does not atttempt to sort them.

If you happen to know your eigenvalues are all real-valued, just use the sort
function to put them in decreasing order. Of course you would undoubtedly
want to rearrange the eigenvectors in the same way so as to preserve the
appropriate pairings of eigenvectors with matching eigenvalues.

Roger Stafford

Re: arrengment of eigenvalu and eigenvector

Bruno Luong — Tue, 01 Jan 2008 10:52:04 -0500

"mustafa alheety" <alheety@yahoo.com> wrote in message
<flco7r$ieu$1@fred.mathworks.com>...
> Dear all...
> Hello...
>
> happy new year frist. please i want to ask if that
> possible in matlab to give my the eigenvalue and eigen
> vector arrengement decreasing

I have sone a small m-file for you.

Bruno

function [varargout]=seig(varargin)
% function [varargout]=seig(varargin);
% SEIG sorted Eigenvalues and eigenvectors.
% Calling: similar MATLAB builtin EIG with optional
% last parameter can be 'ascend' or 'descend'
% for sorting purpose
%
% Related function eig and sort
%

vin=varargin;
sopt='';
% Look where as last argument is 'ascend' or 'descend'
if length(varargin)>=2 && ischar(varargin{end})
    sopt=lower(varargin{end});
    switch sopt
        case {'ascend' 'descend'}
            vin=varargin(1:end-1);
    end
end

nout=max(nargout,1);
varargout=cell(1,nout);
[varargout{:}]=eig(vin{:}); % call eig

if ~isempty(sopt)
    if nout==1 % Calling with 1 output
        varargout{1}=sort(varargout{1},sopt);
    else % Calling with 2 outputs
        [ds is]=sort(diag(varargout{2}),sopt);
        varargout{2}=diag(ds);
        varargout{1}=varargout{1}(:,is); % rearrange
eigen-vectors
    end
end