Polynomial Curve Fitting Function

Hi, I have some problem regarding the polynomial curve fitting. I compute coefficient from Data A using fifth degree polynomial and the sample coefficient obtained from Data A was used back to Data B (to reconstruct similar to Data A). My question is did the polynomial considered my Data B also to fit the curve ?

Answer 1

[KSSV]

No it will not consider data B. It gives polynomial coefficients based on Data A. If your data B x ranges are same as data A x ranges, then data B can be fitted with this polynomial.

[farah]

Ya Data A and B are in same ranges. So the curve fitting didn't considered my Data B? How about the goodness of fit is it consider the Data B?

[KSSV]

As the x range's of both the data's are same. Using the coefficients, it will find the respective y values. Fit will be good.

[farah]

I understand. So the fit will be good. Actually my project is to reconstruct the Data B to be exactly like Data A. But then I don't know how to conclude that since the curve fitting doesn't consider my data B. Do you have any idea?

[KSSV]

Attach your data...this is not a tough job..

[farah]

Hi, KSSV I have email you my data. Can you check it for me? I don't know how to conclude that.

[farah]

If let say I have 4 sample cycle of sine wave. can polynomial work for this wave?

[Walter Roberson]

sine wave requires infinite degree polynomial to fit.

A fifth degree polynomial has at most 5 real-valued zero crossings. 4 cycles of a sine wave has crossings at 0, Pi, 2*Pi, 3*Pi, 4*Pi, 5*Pi, 6*Pi, 7*Pi, and ends one sample before 8*Pi, which is 8 crossings. Therefore a fifth degree polynomial would have to show very noticeable differences than 4 full cycles of sine.

[farah]

so how to to compute that sine wave?

[Walter Roberson]

x = linspace(0, 4*2*pi, 501);
x(end) = [];    %4 cycles would not touch 0 a fifth time
S4 = sin(x);