Origin Ver. and Service Release: 8.5 Operating System:windows 7
I have a set of data going to be fit in function y=a*x^b as shown in fig.1
So I selected the built in function allometric1 as the fitting function. As a result of proper initialization, we had well fitting curve immediately without clicking iteration.
However, after I chosen iteration, the results were getting worse. The fitting curve will be converged as the following figure.
I cannot figure out how'd this happen. Does anyone can give me some suggestions? Many thanks in advance.
I suspect that visually strange, but numerically it probably makes sense because your Y scale is Log10-base. Data points near low boundary contribute little to the Chi^2. I see the Chi^2 value is huge, and immediately iteration has stopped one step after initial parameters. (You can change the Y scale to linear to see the "real" fitting situation.)
I suggest you convert your Y values to their log values, then apply to the appropriate function.
nonlinear fitting getting worse after iteration
Posted - 01/24/2013 : 02:15:02 AM
