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MathGroup Archive 1995

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Fitting data on a vertical line

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg1548] Fitting data on a vertical line
  • From: phpull at unix1.sncc.lsu.edu (Joe Wade Pulley)
  • Date: Sat, 24 Jun 1995 03:47:48 -0400
  • Organization: Louisiana State University

Hello,
	I have recently accidentally asked Mathematica to do a linear
least squares fit to a set of data which were exactly vertically
placed.  Instead of giving me an error or an infinite slope,
Mathematica spits out some sort of fit which is totally wrong.
For example,  if I make up a list of data which is similar to mine, I
get the following results.



In[1]:=
ls={{2.1,3},{2.1,4},{2.1,5},{2.1,6},{2.1,7}}

Out[1]=
{{2.1, 3}, {2.1, 4}, {2.1, 5}, {2.1, 6}, {2.1, 7}}

In[2]:=
ft=Fit[ls,{1,x},x]

Out[2]=
0.924214 + 1.94085 x

Obviously, this equation does not "fit" the data I have given.  The
equation x=2.1 would.  Can anyone explain this very unusual behavior.
--
Joe Wade Pulley			 Department of Physics and Astronomy
Louisiana State University
Baton Rouge, LA 70803		 phpull at unix1.sncc.lsu.edu


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