4.56 FAQ-768 How can I get the fitting parameter values in nonlinear fit at each iteration?

Fit-Parameters-Each-Iteration

Last Update: 7/25/2018

You can use the Labtalk function Nlbegin and Nlfit to perform nonlinear fit, and get the fitting parameter values in nonlinear fit at each iterations.

// import sample data into a new book
newbook;
fname$=system.path.program$ + "Samples\Curve Fitting\Exponential Growth.dat"; //prepare data
impASC; 
// Start a fitting session;
 
 
nlbegin iy:=2 func:=ExpDec1 nltree:=tt;
getnumber -s (Input the iterations) n;     //Construct a dialog to enable user enter the iteration he want to perform
double aa=0;
 
 
loop (i,1,n)
{
	nlfit $(i);  //run the i-th iteration of fitting

	type "The parameter value in $(i) iteration";  
	 
	type "y0= $(tt.y0, %4.6f)";  //output the parameter values
	type "A1= $(tt.A1, %4.6f)";
	type "t1= $(tt.t1, %4.6f)";

	if (tt.fitstatus == 100)
	{
		type "Fit converged, no more iteration will be done";  
		break;
	}
}
 
nlend;

When you enter value 8 in iteration input box when you run the script, you can get the results similar to this:

The parameter value in 1 iteration
y0= -0.162869
A1= 1.283508
t1= -0.998789
The parameter value in 2 iteration
y0= -0.038538
A1= 1.195022
t1= -0.968684
The parameter value in 3 iteration
y0= -0.038365
A1= 1.194898
t1= -0.968641
Fit converged, no more iteration will be done

Keywords:LabTalk, nonlinear fitting, iteration, fitting parameter