[Insight-users] Re: vnl_powell: three parameter fit (Mathieu Malaterre)

[Mathieu Malaterre]

Hi Markus,

  Thanks for the comments. I am also currently investigating LM, as it
seems very promising. Unfortunately I cannot figure out how to use it.
According to:

http://paine.wiau.man.ac.uk/pub/doc_vxl/books/core/book_6.html#SEC44

  I think the vnl implementation lack general implementation and only
provide least square API (need to decompose my function as a sum of
square function...). See my post:

http://sourceforge.net/mailarchive/forum.php?thread_name=bf0c3b3f0705150506q527466a4jc530bf42455f540c%40mail.gmail.com&forum_name=vxl-users

  I am waiting for a vnl guru to confirm the vnl - LM optimizer cannot
do general cost function minimization.

  In which case I am going now toward a lbfgs approach. I can compute
the first derivative of my function, and it would be dumb not to use
this information (powell method is too generic).

  A final note. I could get powel to converge to the correct solution
when giving the optimizer a relative close solution. I was not able
(read: I don't have the time to dig in powell theory) to figure out
'how good' my initial solution should be.

I'll let you know how it goes,

Thanks for your interest,
-Mathieu


On 5/15/07, m.weigert at fz-juelich.de <m.weigert at fz-juelich.de> wrote:

> Hi Mathieu,
>
> I think there is also a Levenberg-Marquardt implementation in ITK which may be better suited to
> perform non-linear least squares fits.
> I don't know how to do this with vnl_powell, I am currently investigating Levenberg-Marquardt for
> parameter fitting.
>
> Kind regards,
> Markus
>
>


-- 
Mathieu