| T O P I C R E V I E W |
| RafaelVS |
Posted - 03/19/2015 : 3:31:53 PM
Hello. I am trying to plot an exponential function like this
where V=y(x) and r=r(x), and a, Z1, Z2, e are constants I need to find.
How can I define a exponential function y = (k/x)exp(-x/a) so that Origin can give me k and a?
I'm using Origin 8.1 |
| 6 L A T E S T R E P L I E S (Newest First) |
| AndreDourado |
Posted - 04/24/2015 : 12:41:57 PM
Hi,
I wrote, on Origin 9.0, the function y=A*exp(-B*x)+C*x*exp(-B*x).
It worked twice, but with other data the report error said that it could not converge and that the reason was unknown. Once it said that the parameter were not independent and that I should try to fix one of them, what is not possible to me. What can I do?
Thank you!
André |
| Hideo Fujii |
Posted - 04/17/2015 : 5:05:34 PM
Hi,
Here is the Origin document about the Nonlinear Implicit Curve Fitting:
http://www.originlab.com/doc/Origin-Help/Fitting-Implicit
which also contains a table of comparison between the Levenberg-Marquardt and the Orthogonal Distance Regression, and the reference of later case. Sorry I haven't originally realized that your version doesn't have this feature. You can download the evaluation version of Origin 2015 to try out this method: http://www.originlab.com/demodownload.aspx
--Hideo Fujii
OriginLab
|
| RafaelVS |
Posted - 04/17/2015 : 3:37:49 PM
Hi Hideo Fujii!
That's impressive!! But could you explain it a little more? I didn't quite understand what you did! |
| Hideo Fujii |
Posted - 04/17/2015 : 3:05:20 PM
Hi Rafael,
When a part of the curve is very steep (near 0 in your case), the residual's contribution would become
too high and sensitive to the parameters, even though the Chi square may be numerically minimum. To consider
both X and Y directions, you can try to define the fitting function as implicit. Please look at my trial below:
(To make my life easier, I have plugged your parameter values in the definition of this function.)
--Hideo Fujii
OriginLab
P.S. Sorry for that the orthogonal regression for implicit functions has become available in the version 9.0 and later, and only in Pro versions. |
| RafaelVS |
Posted - 04/17/2015 : 2:05:14 PM
Hi, I read and did everything in those links but still the best plot I've got was this one:
Is there any way to improve it? |
| JacquelineHe |
Posted - 03/20/2015 : 04:10:40 AM
Hi,
If you want to get the parameters in a user-defined function, you can:
1. In Origin 8.1, you could define a fitting function in Fitting Function Organizer dialog.
Set
http://www.originlab.com/doc/Origin-Help/FitFunc-Organizer-Builder
http://www.originlab.com/doc/Origin-Help/FitFunc-Organizer
Please refer to the Video Tutorial:
http://www.originlab.com/Index.aspx?go=Support/VideoTutorials&pid=1172
2. Highlight your dataset (X and Y), select “Analysis:Fitting:Nonlinear Curve Fit” to open the “NLFit” dialog.
In the “Function Selection” page, choose “Category” and “Function” that you defined. Then do fitting to get the parameter value.
Please refer to the Video Tutorial:
http://www.originlab.com/Index.aspx?go=Support/VideoTutorials&pid=1564
Thanks
Jacqueline
OriginLab |
