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MathGroup Archive 2004

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Nonlinearfit (real function with complex entries)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg50003] Nonlinearfit (real function with complex entries)
  • From: alex_punnoose at yahoo.com (Alex)
  • Date: Wed, 11 Aug 2004 05:52:57 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

I have a real function whose individual terms are complex 
(they sum up to a real number). The functions involved are
digamma functions and trigonometric.

When I use this function in NonlinearFit, I get the following
error:

FindMinimum::"fqnum": "Objective function or gradient is not real

General::"stop": "Further output of FindMinimum :: "fqnum" will be 
suppressed during this calculation."

I guess the problem is that the function is real only upto an
infinitesimally small imaginary part ( of the order 10^{-16} ) set 
by the machine accuracy. 

I tried the following: Chop, ComplexExpand, Re, defining the 
derivates explicitly and then chopping it and a lot of other things.

Could someone out there please help me?

Thanking you in advance - alex


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