Hi, I'm trying to fit some data to a function of degree 4 or 5, but when I
plot it, it doesn't fit:
DATA:
C30 =
0.063330 0.057200 0.052870 0.047380 0.044860 0.039710
0.037070 0.036030 0.034990
t =
1.0000 1.5000 2.0000 3.0000 5.0000 7.0000 10.0000
13.0000 18.0000
FIT:
p=polyfit(t,C30,4)
0.0000027990 -0.0001193780 0.0018221783 -0.0125401220 0.0727802050
The problem is that when I plot(t,C30) and plot(p) I get totally different
curves, am I missing somethiing???
--
Sent from: http://octave.1599824.n4.nabble.com/Octave-General-f1599825.html
Hi T.G.,
Yes, I believe it is safe to say that you are missing something. Look at vector that is returned from polyfit that you print out:
p=
0.0000027990 -0.0001193780 0.0018221783 -0.0125401220 0.0727802050
these are the coefficients of the polynomial (see help polyfit for more explanation). And the "curve" from plotting that vector is just the coefficients wrt their index. The function you're probably looking for is polyval (help polyval for info) so that you can evaluate the fitted curve at the values of x that you want.
Hope this helps,
James Sherman Jr.