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MathGroup Archive 1997

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Re: Questions on fitting and plotting data

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7981] Re: [mg7952] Questions on fitting and plotting data
  • From: seanross at worldnet.att.net
  • Date: Wed, 30 Jul 1997 23:57:32 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Daniel Goscha wrote:
> 
> I am *very* low on the Mma learning curve so this may be obvious, but
> here is what I am trying to do.  I have a set of data that I want to
> plot, fit, and then plot the fit over it.  The problem I am having is
> getting the correct fit and getting it to plot.  Here is what I have so
> far...
> 
> In[38]:=
> t2 = {{1, 1.5, .5}, {2.3, 2.8, .5}, {3, 3.7, .5}, {4.2, 4.6, .5},
>   {5.1, 5, .5}, {6.4, 6.4, .5}, {7.2, 7.7, .5}, {8, 8.9, .5}}

> **now, here is where I start getting the problems - this is obviously
> NOT the correct least-square fit solution to the data I have
> specified.**
> 
> In[40]:=
> fit1 = Fit[t2, {1, x }, {x, y}]
> Out[40] =
> 0.5-5.55112x10^-17 x


I assume that your data in t2 is of the form {x,y,f}?  If so, when you
set up your fit, you specify that 1 and x are your basis functions. 
Didn't you want y as a basis function as well?

Try something like fit1=Fit[t2,{1,x,y},{x,y}] to have it use both x and
y in a fitting routine.


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