[lisplab-devel] Eigenvalues

[José Santos]

Hi Jørn,

Thanks for the reply.

After some more trial and error and Matlab vs Lisplab output, I managed to
identify the value
I'm interested in: the last in the Lisplab return value, which consistently
matches the second value in the Matlab array.

Thanks again.

Sincerely,
José Santos

On Tue, Mar 19, 2013 at 7:58 PM, Jørn Inge Vestgården <
jivestgarden at gmail.com> wrote:

> Dear José Santos
> What you describe looks like a bug in lisplab since eigenvalues should
> basically just call dgeev.
>
> The reason for for the bug is probably that lisplab has some functionality
> to switch between native and foreign implementations when both are present.
> In the case of eigenvalues, there is no native lisp implementation, but it
> might be that it thinks that it exists.
>
> The matlisp code is, as the name implies, basically taken from Matlisp.
> Unfortunately I have not put much emphasis on testing it and making
> high-level interface functions. Hence it is prone to get bugs.
>
> Best Regards
> Jørn Inge Vestgården
>
>
>
> 2013/3/15 José Santos <jsmpereira at gmail.com>
>
>>  Hi,
>>
>> After trying out GSLL, Clem, also FemLisp, Lisplab managed to get me
>> the functionality I needed with the least trouble.
>>
>> I'm trying to get the connectivity of a graph (second smallest eigen
>> value) from eigenvalues.
>>
>> Given the fully connected 4x4 adjacency matrix:
>>
>> #md(( 0.000      1.000      1.000      1.000    )
>>     ( 1.000      0.000      1.000      1.000    )
>>     ( 1.000      1.000      0.000      1.000    )
>>     ( 1.000      1.000      1.000      0.000    ))
>>
>> I compute the diagonal matrix of the vector sum of the adjacency matrix
>> and then
>> subtract the adjacency matrix from it to get the laplacian matrix.
>>
>> I'm unable to call (lisplab:eigenvalues) on that matrix, despite being a
>> #md matrix.
>> I can see that the function calls for LISPLAB::MATRIX-FOREIGN-DGE.
>> However other functions
>> that call for the same type seem to work when called with #md, namely
>> FFT1.
>>
>> As a workaround, I'm using this call to get the eigenvalues:
>>
>> (lisplab::dgeev (laplacian-matrix *adj-matrix* *diag-matrix*) nil nil)
>> and I get:
>>
>> (
>> #md(( 4.000    )
>>     (-1.1102d-16)
>>     ( 4.000    )
>>     ( 4.000    ))
>>  NIL NIL)
>>
>> Is this appropriate?
>>
>> I'm curious however about different results I get from Matlab.
>> I get the same results up until the call to
>>
>> >> eig(diag(sum(A)) - A)
>>
>> which gives me
>>
>> ans =
>>
>>     0.0000
>>     4.0000
>>     4.0000
>>     4.0000
>>
>> Any comment I can get on this would be awsome. Am I going about this
>> right?
>> What might I be missing?
>>
>> Sorry about the lengthy email.
>>
>> Thanks!
>> José Santos
>>
>> _______________________________________________
>> lisplab-devel mailing list
>> lisplab-devel at common-lisp.net
>> http://lists.common-lisp.net/cgi-bin/mailman/listinfo/lisplab-devel
>>
>>
>
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