Re: Fitting to complex values
- To: mathgroup at smc.vnet.net
- Subject: [mg30801] Re: Fitting to complex values
- From: "Lawrence A. Walker Jr." <lwalker701_remove_ at earthlink.net>
- Date: Wed, 19 Sep 2001 00:16:41 -0400 (EDT)
- References: <9nalpb$npj$1@smc.vnet.net> <9ncgqf$q1g$1@smc.vnet.net> <9nf6i0$sfj$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi Kevin,
Both NonlinearFit and Fit functions perform the least squares fit. I
found that both can be used on complex data directly. Its just that Fit
does it with basis functions that are linear combinations and
NonLinearFit does it with a function you pick. The method I proposed is
one of perhaps many. I chose this method because I felt it offered the
flexibility in that the real part and imag part may very well have
distinct behaviors which is conducive for two distinct functions or models.
On a side note however, I kept getting the following error when I tried
to use NonlinearFit on the complex data directly:
"Less::nord: Invalid comparison with ... attempted." Yet, Mathematica
returned an 'exceptable' solution. Should I disregard the error message?
Thanks,
Lawrence
Kevin J. McCann wrote:
> What about just doing a least squares fit? I have done this for complex data
> and it works fine.
>
> Kevin
>
> "Lawrence A. Walker Jr." wrote:
>>Hi Max,
>>
>>Try dividing the complex data into two data sets: real and imaginary.
>>Then you can apply the NonlinearFit function twice.
>>
>>For example
>>
>>data = {{1, 1+2 I},{2, 3+4 I}, {3, 4+5 I}};
>>dataRe=Map[{#[[1]],Re[#[[2]]]}&,data];
>>dataIm=Map[{#[[1]],Im[#[[2]]]}&,data];
>>
>>NonlinearFit[dataRe, func1, ...];
>>NonlinearFit[dataIm, func2, ...];
>>
>>Note, you must specify the functions apriori.
>>
>>Lawrence
>>
>>
>>Max Ulbrich wrote:
>>
>>
>>>Hi,
>>>
>>>I have complex data (re+im) from a lock-in amplifier and want to fit
>>>them
>>>to a complex function. Though, the NonlinearFit function doesn't work
>>>with complex data. Has anyone a solution?
>>>
>>>Max
>>>