3.146 FAQ884 How to get a good fit with a very large or a very small parameter?goodfitforlargesmallparam
Last Update: 9/22/2017
When you do curve fitting, you might meet these problems:
 Origin returns missing value in standard errors when you perform fitting with a large parameter.
 Fit can not converge when you perform fitting with a very small parameter.
In both cases, we need to redefine the equations to avoid a very large or a very small parameter. For example:
 ; if A is a large parameter, we can redefine the equation as . After fitting, we can get ;
 ; if A is a small parameter, we can redefine the equation as . After fitting, we can get ;
Another actual example is the nonlinear implicit diode function:
, k is in as a unit.
To do fitting with this function, firstly, we can reset the parameter to , where , then the parameter won't be too small.
In this way, we can avoid the very small parameter and finally get the fit converge.
Keywords:good fit, not converge, missing value in standard error,diode function
