curve fitting tool box
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Hi all,
there is something i don't understand in the curve fitting tool box, i have :
x= [1 2 3 4];
y= [1 2 3 4];
after using the curve fitting tool box this is the results comes out:
Linear model Poly1:
f(x) = p1*x + p2
where x is normalized by mean 3.5 and std 1.871
Coefficients (with 95% confidence bounds):
p1 = 1.871 (1.871, 1.871)
p2 = 3.5 (3.5, 3.5)
Goodness of fit:
SSE: 2.81e-30
R-square: 1
Adjusted R-square: 1
RMSE: 8.382e-16
the plotted graph on the right is correct but the resulted equation is not correct !!!!! ??
Thanks.
1 Comment
Tom Lane
on 1 Aug 2013
What do you do with the Curve Fitting Toolbox? If I type
fit(x',y','poly1')
I get a slope of 1 and an intercept that is zero (tiny number).
Answers (1)
dpb
on 2 Aug 2013
Edited: dpb
on 2 Aug 2013
Of course the equation is right--as the message says p1 and p2 are coefficients for the normalized x. Substitute in z=(x-3.5)/1.871 and solve for m and b in terms of z and you'll find that
m=p1/1.871 --> 1
b=p2+3.5 --> 0
In the tool it's the "Center and Scale" checkbox that controls it; at the command line the fit option 'Normalize', 'on|off'
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