Discover MakerZone

MATLAB and Simulink resources for Arduino, LEGO, and Raspberry Pi

Learn more

Discover what MATLAB® can do for your career.

Opportunities for recent engineering grads.

Apply Today

New to MATLAB?

curve fitting tool box

Asked by ahmed

ahmed

on 31 Jul 2013

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

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).

ahmed

ahmed

Products

No products are associated with this question.

1 Answer

Answer by dpb

dpb

on 2 Aug 2013
Edited by dpb

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'

0 Comments

dpb

dpb

Contact us