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Re: Problems with FindMinimum

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90722] Re: Problems with FindMinimum
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Mon, 21 Jul 2008 04:29:18 -0400 (EDT)

On 7/20/08 at 6:32 AM, teodorom at hotmail.com wrote:

>Hi, I'm having problems with the FindMinimum. I'm currently getting
>errors like this: FindMinimum::nrlnum: The function value
>{0.335521+43899.8 \ [ImaginaryI],0.376043+43899.8
>\[ImaginaryI],0.424669+43899.8 \ [ImaginaryI],<<6>>,0.311208+46311.9
>\[ImaginaryI],<<27>>} is not a list of real numbers with dimensions
>{37} at {x0,y0,x1,y1,hh0,hh1} =
>{0.00580647,-2.13969*10^20,-9.86301*10^-6,1.23875*10^20,-30574.3,19.
>6042}. I guess this happens because the function I'm trying to fit
>with experimantal data, gets imaginary values for some values of the
>parameters. How can I avoid this and get meaningful results ?

If you truly expect a response that is better than your guess
you need to provide more details such as what is the function
you are trying to fit?

Meanwhile, there are a variety of things you could try such as:

Specifying the method for FindMinimum to use rather than
accepting the result
Use NMinimize with appropriate constraints instead of FindMinimum
Use FindFit instead of FindMinimum

=46indFit is designed to fit a function to data. As a general
rule, you will get better results with Mathematica when you use
things more specific to your task than the more general things.


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