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Re: Fitting step function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122098] Re: Fitting step function
  • From: Virgil Stokes <vs at it.uu.se>
  • Date: Thu, 13 Oct 2011 03:49:20 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201110120744.DAA16264@smc.vnet.net>

On 12-Oct-2011 09:44, premiumxy wrote:
> Hello,
>
> I have the following problem: I have a set of data about some phase information of a signal. At certain points there is a clear step of 180 degrees.
These "certain points" might be due to phase wrapping and can be caused by the 
discontinuity in the arctan function. Perhaps, worth at least looking at before 
going in further with your problem.
>
> I would like to fit this data to find the x-coordinates of these steps. I have the feeling that "normal" step-functions in Mathematica (such as UnitStep, HeavisideTheta, Sign...) are not varied in the fit-routines (such as NonlinearModelFit). I guess it this is caused by the functions not being continuous.
>
> I would appreciate any hints for this quite simple (?)problem. The only option that I can currently see is to create a "step-like" continuous function such as Tanh[A x] (with A>>1)
>
> Thanks!
>
Best regards :-)




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