[Insight-users] derivative calculation

[Michael]

Hi,

I've noticed, that the for the derivative calculation, the 
MeanReciprocalSquareDifferenceImageToImageMetric and the 
GradientDifferenceImageToImageMetric make uses of a fix-coded (0.00011) 
delta for their derivative calculation. It seems to me, that the 
HistogramImageToImageMetric uses a flexible derivative step length and 
scalings for each parameters dimension for the same thing. I hope I 
understood this correctely...

Is there a reason for the fix coded 0.00011 delta, and why 0.00011?

Thanks,

Michael