| Author |
 Topic  |
|
|
andhen
Posts |
 Posted - 10/12/2006 : 12:58:03 PM
|
Origin Version: OriginPro 7.5 SR0
Operating System: WinXP
I need to fit my data to a cubic equation of the type:
0 = ax^3 + bx^2 + cx + d
I found the "find roots" project, but don't know how (or whether it is possible?) to implement it to the NLSF fitting. The constants a,b,c,d should include the fitting parameters as well as the y-values. Can somebody help? |
|
|
larry_lan
China
Posts |
Posted - 10/12/2006 : 10:20:50 PM
|
Hi
The "find roots" project can not do the symbolic computation, maybe you can try some other tools like MatLab to solve the equation.
Larry
OriginLab Technical Services |
 |
|
|
verrallr@a
Canada
44 Posts |
Posted - 10/16/2006 : 2:43:39 PM
|
You can use TableCurve 2D
http://www.systat.com/products/TableCurve2D/
at this address (you can try with a downloaded trial version).
Or, possibly, with Origin NLSF, you could take the cube root of one of your y values to get an approximate solution for the "a" and take b,c,d as zero. That probably would only work if the ax^3 represents a large part of the true value.
Richard |
|
|
|
ireneh
USA
Posts |
Posted - 10/22/2006 : 10:20:04 PM
|
If you are using MATLAB then it can be done very easily, just two commands "polyval" and "polyfit". You may be able to find more on http://www.kluid.com . You can also use generic version of matlab, known as OCTAVE and its available for free on their website.
Irene
Edited by - ireneh on 10/22/2006 10:22:45 PM |
|
|
|
Mike Buess
USA
3037 Posts |
Posted - 10/23/2006 : 07:53:34 AM
|
As discussed in this topic, an exact solution to the cubic equation can be used in Origin (or elsewhere) to find x for any a, b, c and d.
Mike Buess
Origin WebRing Member |
|
|
| |
Topic |
|
find roots and fitting