MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: How to fit complex valued data?

  • To: mathgroup at
  • Subject: [mg64147] Re: [mg64096] How to fit complex valued data?
  • From: Bob Hanlon <hanlonr at>
  • Date: Thu, 2 Feb 2006 02:17:05 -0500 (EST)
  • Reply-to: hanlonr at
  • Sender: owner-wri-mathgroup at

You could try fitting the absolute value since it depends on both the real and 
imaginary parts. You must test the result since you might get the sign of b 

expr[b_,x_]:=(1+I b x)^-1;







{b -> 0.9831217471019714}

Bob Hanlon

> From: James McCambridge <James.McCambridge at>
To: mathgroup at
> Subject: [mg64147] [mg64096] How to fit complex valued data?
> Esteemed Colleagues,
> I would like to fit a complex valued data set with FindFit (I'm willing to 
> try other methods too, but I thought I'd start out with the basics). Is 
> this possible? 
> For example, I am interested in fitting the complex permittivity of liquid 
> polymers vs frequency, which has a functional form:
> In[1]:=    expr[b_,x_]:=(1+I b x)^-1;
> Using this form to generate data, with b = 1.0, I get:
> In[2]:=    data ={{1,0.5 -0.5 I},{2.,0.2 -0.4 I},{3.,0.1 -0.3 I
> },{4.,0.0588235 -0.235294 I},{5.,0.0384615 -0.192308 I},{6.,0.027027 
> -0.162162 I},{7.,0.02 -0.14 I},{8.,0.0153846 -0.123077 I},{9.,0.0121951 
> -0.109756 I},{10.,0.00990099 -0.0990099 I}};
> Using FindFit, I come up against an error message.
> In[3]:=   FindFit[data,expr[b,y],{{b,1.}}, y]
> has the output
> Out[3]:=   FindFit::nrlnum: The function value {0.+0. I, 0.+0. I, -1.38778 
> 10^-17+0. I, <<4>>, 0.+0. I, 0.+0. I, 0.+0. I} is not a list of real 
> numbers with dimensions {10} at {b} = {0.}
> The form expr[0.,x] doesn't look poorly behaved, so what gives?
> I could separately fit the real and imaginary components, but this often 
> gives two somewhat different sets of parameters; I would like to obtain 
> the parameters which optimize the fit to BOTH the real and imaginary 
> parts.
> Your comments and suggestions are greatly appreciated!
> Jim McCambridge
> This communication is for use by the intended recipient and contains
> information that may be Privileged, confidential or copyrighted under
> applicable law. If you are not the intended recipient, you are hereby
> formally notified that any use, copying or distribution of this e-mail,
> in whole or in part, is strictly prohibited. Please notify the sender by
> return e-mail and delete this e-mail from your system. Unless explicitly
> and conspicuously designated as "E-Contract Intended", this e-mail does
> not constitute a contract offer, a contract amendment, or an acceptance
> of a contract offer. This e-mail does not constitute a consent to the
> use of sender's contact information for direct marketing purposes or for
> transfers of data to third parties.
> Francais Deutsch Italiano  Espanol  Portugues  Japanese  Chinese  Korean

  • Prev by Date: Re: does anybody know how to find the inverse Laplace transform of this wierd thing?
  • Next by Date: Trigonometric form of complex numbers
  • Previous by thread: Re: How to fit complex valued data?
  • Next by thread: How to evaluate the following expression in Mathematica?