[Insight-developers] Numerical methods: an example of places that need improvement.

[Jim Miller]

I guess for certain problem sizes where the problem is well conditioned it shouldn't matter too much. But I imagine in the bspline code this is a hefty system of equations. 



On Nov 3, 2010, at 3:38 PM, Luis Ibanez <luis.ibanez at kitware.com> wrote:

> From our tcon on image registration.
> 
> 
> The following code:
> 
>   vnl_matrix<double> B = 
>     vnl_matrix_inverse<double>( N_matrix.transpose() * N_matrix) * N_matrix.transpose() * data_matrix;
> 
> is from 
> 
> Insight/Code/Common/
> itkNonUniformBSpline.txx
> (line 313).
> http://public.kitware.com/cgi-bin/viewcvs.cgi/Code/Common/itkNonUniformBSpline.txx?revision=1.9&root=Insight&view=markup
> 
> 
> It is trying to solve the linear system
> 
>              X  = N * B
> 
> by doing:
> 
>         B = ( N' * N )^-1  *  N'  * X
> 
> 
> instead of invoking one of the linear solvers
> that we are carrying in ITK via VXL.
> 
> 
> ----
> 
> 
>    Luis
> 
> _______________________________________________
> Powered by www.kitware.com
> 
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
> 
> Kitware offers ITK Training Courses, for more information visit:
> http://kitware.com/products/protraining.html
> 
> Please keep messages on-topic and check the ITK FAQ at:
> http://www.itk.org/Wiki/ITK_FAQ
> 
> Follow this link to subscribe/unsubscribe:
> http://www.itk.org/mailman/listinfo/insight-developers
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.itk.org/mailman/private/insight-developers/attachments/20101105/eafa228b/attachment.htm>