| T O P I C R E V I E W |
| right |
Posted - 06/16/2003 : 02:42:08 AM
I need to find the equation of a dataset that i have, when plotted looks like a parabolic curve.
here is the data
x y
0.1 28.8707
0.2 17.3049
0.3 13.4001
0.4 11.4265
0.5 10.234
0.6 9.42635
0.7 8.86566
0.8 8.43657
0.9 8.11447
1 7.85629
I've tried the non-linear curve fitting by creating my own equation P1/(p2+x), but i can't seems to get a nice fit for my curve.
Can someone please help or is there is other ways to do this?
thanks |
| 4 L A T E S T R E P L I E S (Newest First) |
| edgar.kaiser |
Posted - 06/18/2003 : 04:48:54 AM
Hello Right,
your data looks like a hyperbola and not a parabola. Also your own model function is hyperbolic with a pole at x = -p2.
A parabola has a model function y = p0 + p1*x + p2*x2
Maybe you should introduce an y-offset into your hyperbolic model:
y = p0 + p1/(p2 +x)
This model is not forced to approach zero for large x-values. Also an exponential with y-offset might work as Mike suggested.
Regards,
Edgar |
| Mike Buess |
Posted - 06/16/2003 : 10:42:25 AM
P1/(P2+x) works fine in Origin 7 if I uncheck Use Origin C and use Expression for the function form. Even so, your data fit an exponential much better.
Mike Buess
Origin WebRing Member
Edited by - Mike Buess on 06/16/2003 10:43:11 AM |
| right |
Posted - 06/16/2003 : 10:20:30 AM
but I am expecting a parabolic curve.
can someone please guide me on how to do that.
I know how to use a polynomial fit, but that's not what i want. |
| easwar |
Posted - 06/16/2003 : 09:44:12 AM
Hi,
If you wish to use NLSF, there is a polynomial category that has a built-in parabola function that you can make use of. The data does nt look very "parabolic" - perhaps you can get better/desired fits if you fix parameters and/or place lower/upper bounds etc. if doing so makes sense for your data/measurement.
Note that you can also use the Analysis->Fit Polynomial menu to perform the fit.
Easwar
OriginLab.
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