Nonlinear material model fit

Hello there,

I have a few model functions, for example: y=2(x^2-1/x)(C1+C2/x).

I need to fit the parameters for a table of tension test data.Also, i would like to use different error functions, not just least root means square. How can i solve that?

Don't even know how to go about it.

Thanks

Answer 1

[Image Analyst]

fitnlm() is one of my favorite MATLAB functions. See my attached demos where I use fitnlm() to fit a variety of different functions. I think you'll be able to figure out how to make changes. If you can't, then attach some sample data and I'll modify the demo for you.

[Kálmán Németh]

Thank you, however i have some questions.

Can i somehow prescribe for the parameters to be positive values or between some value? Also can i modify the error function used in this method?

[Image Analyst]

If you can, I don't know how.