| T O P I C R E V I E W |
| mvodw |
Posted - 07/29/2011 : 11:17:11 AM
Origin Ver. 8.0951
Operating System: Win 64 bit
Hello origin community,
i want to fit my data points with a own funktion but i have some trouble with it.
The funktion is:
y = A - B * [1 - exp(-C * sqrt(x)]
The problem is i dont know what exactly to type in the parameter options and the parameter initialise boxes.
Would be very nice if someone could tell me what to write in.
The parameter A should be something between 0.6 and 0.8.
B is something like 0.9 to 1.2.
This both parameters are the important values wich i wanted to know exactly for each of my data sets. C is unimportant for my work but a needed parameter to fit the curve.
Greeting Malte |
| 1 L A T E S T R E P L I E S (Newest First) |
| Hideo Fujii |
Posted - 07/29/2011 : 2:14:34 PM
Hi Malte,
You can set the lower and upper bounds for parameters you want in NLFit fitting tool by the following:
1) In NLFit, choose "Bounds" tab, double-click the cell of "LB" (or "UB") for the parameter; Each double-clicking cyclically change between empty, "<=" and "<". Choose either "<=" or "<".
2) Double-click the cell of "LB Value" (or "UB Value"), and enter the lower (or upper) parameter value such as 0.6 for A.
3) Make sure that the values of all parameters are filled (i.e. non the missing value "--"). If you still have "--" for some parameters, fill their initial estimates (a middle value between lower- and upper bounds).
4) You can check the current goodness of parameters visually by pressing Chi^2 button. If the curve is good enough, you can run fitting by pressing "Fit until converged" button.
Hope the above explanation is helpful.
--Hideo Fujii
OriginLab
P.S. You cannot use [...] in the definition of your user-defined function, and you have to use (...), instead. Therefore, you can define, say by Fitting Function Organizer (or Fitting Function Builder in ver. 8.5.1).
y = A - B * (1 - exp(-C * sqrt(x))) |
|
|
