a neat idea, easy to do in Maxima, perhaps. Numerical derivatives



    *Accurate numerical derivatives in MATLAB*

	
*Source*
	ACM Transactions on Mathematical Software (TOMS) archive 
<http://portal.acm.org/toc.cfm?id=J782&type=periodical&coll=portal&dl=ACM&CFID=525354554&CFTOKEN=525354554>;
Volume 33 ,  Issue 4  (August 2007) table of contents 
<http://portal.acm.org/toc.cfm?id=1268776&type=issue&coll=portal&dl=ACM&CFID=525354554&CFTOKEN=525354554>;
Article No. 26  
Year of Publication: 2007
ISSN:0098-3500
*Author * 	
L. F. Shampine 
<http://portal.acm.org/author_page.cfm?id=81100197580&coll=portal&dl=ACM&trk=0&CFID=525354554&CFTOKEN=525354554>; 
	 Southern Methodist University, Dallas, TX

*Publisher* 	
ACM <http://www.acm.org/publications>;  New York, NY, USA


The basic observation is that if you can evaluate a function accurately 
at a complex point, you have a way of getting very very accurate 
numerical values of its derivative.

Observe that  Im(  f(x+i*h)) /h   = f'(x)- h^3/6*f'''(x) + ....

solve for f'(x).

Much better than finite differences.  Read the paper if you want more 
interesting observations.
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