Deformable registration in D

[Robert Jacques]

I recently presented at the 49th Annual Meeting of the American  
Association of Physicists in Medicine an application of a deformable  
registration algorithm during the general poster discussion session. Of  
course, the reason I?m posting this here is that I wrote it in D. Or more  
precisely, I refactored it to D from C++, with some surprising results.  
First, the main algorithm dropped to half the lines of code and I was able  
to completely remove some supporting routines. Second, the numerical  
stability of the algorithm increased, helping reduce a major fundamental  
issue/flaw in algorithm (Ah, the joys of a continuous algorithm working on  
discrete data). And lastly, it ran three to four times slower. The culprit  
turned out to be the exponential function, which is the crux of the  
algorithm and also what I assume was responsible for the increased  
stability. I switched to using an exponential with finite support and  
regained the speed while keeping the stability. For reference, I was using  
Microsoft Visual Studio 2003 and D1.x/Phobos on Intel/XP box.
The code is now open source and available at:
http://dailabs.duhs.duke.edu/imagequality.html
And the associated abstract is published in Medical Physics:
http://www.medphys.org/

P.S. Thank you Walter and the community for this great language.