Synopsis
		sfnderiv < Fin.rsf > Fout.rsf order=1 length=5 scale=y axis=1

This program implements Fornberg, 1988
paper for digital differentiators
of arbitrary order.

So, it computes first, second, n derivative along axis 1,2 or 3.

Parameters
		int axis=1 apply differentiator along axis, default is fast axis   int length=5 filter length, the lengthier the accurate, but also gets costlier   int order=1 order of the derivative, default first derivative   bool scale=y [y/n] scales by 1/d^order

Used In
		RSF          rsf/sfnderiv