| Author |
 Topic  |
|
|
RibeiroS
Portugal
3 Posts |
 Posted - 04/14/2017 : 12:26:08 PM
|
Hello guys,
I´m trying to make a nonlinear regression analysis with a user defined function as " y= a* (1- (x / b)) - c* ( b - x + ( x* ln( x / b)) " (in expression option) and when i perform the quick check, this message appears "y = -- (Undefined variable: LN( X / B)". Is there anything i can do to correct this?
Thank you for your help!
Best regards! |
|
|
arstern
USA
237 Posts |
Posted - 04/14/2017 : 3:20:20 PM
|
Hi,
The y = -- (undefined variable) message can appear when you don't input all your parameters and variables correctly. I would recommend checking this first. How did you set up your a,b,c variables?
Below is a link to a tutorial on nonlinear fitting curves:
http://www.originlab.com/doc/Tutorials/UserDef-FitFunc
Thanks,
Aviel Stern
OriginLab |
 |
|
|
RibeiroS
Portugal
3 Posts |
Posted - 04/14/2017 : 8:00:25 PM
|
Hi Aviel,
Thank you very much for the answer. In this case a only wrote a,b,c in the "parameters", once i want all of them to be fitted. After i changed the initial values, quick test and appears this message. I don´t know if i need to defined something more as it seems the problem is in the ln function.
Thank you once again!
Best
Sara |
|
|
|
arstern
USA
237 Posts |
Posted - 04/17/2017 : 09:20:45 AM
|
Hi Sara,
When I input your parameters and equation into the fitting function builder, a y value is produced from the quick check. See image below. Could you please reply with a screen shot of your fitting function builder (maybe of all three steps).
Thanks,
Aviel Stern
OriginLab |
|
|
|
RibeiroS
Portugal
3 Posts |
Posted - 04/17/2017 : 5:32:14 PM
|
Dear Aviel,
It worked! Thank you very much! The reason was a parentheses that was missing in the last part of the expression.
Thanks for the time you spent on this.
Best regards
Sara |
|
|
| |
Topic |
|
Nonlinear regression using ln function