[Insight-users] questions about the mutualinformationHistogramImageToImageMetric

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when I use the histogramImageToImageMetric, for example, the
itkMutualInformationHistogramImageToImageMetric , 
how should the parameters be assigned? particularly, the
metric->SetDerivativeStepLengthScales();and I want to konw 
whether the file *.txx considers that the overlap region is also changed with the
changing transform parameters?
another question: how to assign the parameters of the optimizer such as
regularGradientDescentOptimizer and so on?
Thanks a lot!