Fitting an exponential using nlinfit
68 views (last 30 days)
Show older comments
Matthew on 13 Nov 2015
Commented: Star Strider on 17 Nov 2015
I am trying to fit an exponential fit to some data... I have tried using Nlinfit but don't seem to be getting anywhere
I think the problem is my starting conditions beta0... How do I choose these variables? the error i get is Error using nlinfit>checkFunVals (line 612) The function you provided as the MODELFUN input has returned Inf or NaN values.
Error in nlinfit>LMfit (line 559) if funValCheck && ~isfinite(sse), checkFunVals(r); end
Error in nlinfit (line 276) [beta,J,~,cause,fullr] = LMfit(X,yw, modelw,beta,options,verbose,maxiter); Can anyone point me in the right direction? I would have thought its quite easy but i am not finding the documentation particularly helpful....
Star Strider on 13 Nov 2015
If the values of ‘time_bbdom(:,1)’ are large enough, the ‘exp(-b(3)*time_bbdom(:,1))’ term will be zero, causing the Inf error. Without knowing more, one way to avoid this could be to set the initial value of ‘b(3)’ to ‘max(time_bbdom(:,1))/10’ or some such. You may have to experiment to get the result you want.
Star Strider on 17 Nov 2015
The easiest way I can think of to estimate ‘b(1)’ is to take the mean or max of your data. Experiment with both and use the one that works best.
I don’t have your data or the code you used to implement polyfit, so I can’t comment on them.
More Answers (0)
Find more on Get Started with Curve Fitting Toolbox in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!Start Hunting!