# Surface fitting Classic List Threaded 4 messages Open this post in threaded view
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## Surface fitting

 Hello Everyone I am currently working in a Pchem lab and am trying to model spectroscopy data. I have a 256 x 433 unit matrix of signal data. Each signal is a function of a wavelength value and a time value. So far I have used the functions "nonlin_curvefit" and "leasqr" to fit the data one row(or column) at a time. Now I would like to fit the entire surface to an equation that is a function of both time and wavelength. The inputs of the function leasqr are leasqr(x,y,pin,f). Y will be the 256x433 signal data, pin will be my initial parameter guesses and f will be my function handle. The problem I am having is the x vector(s) for independent values. This is a function of both the wavelength and time variables. What can I put in for the x argument so that the leasqr function fits the entire matrix? Thank you Joel
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## Re: Surface fitting

 On 02/22/2015 09:14 PM, jlapin wrote: > Hello Everyone > > I am currently working in a Pchem lab and am trying to model > spectroscopy data. I have a 256 x 433 unit matrix of signal data. > Each signal is a function of a wavelength value and a time value. > So far I have used the functions "nonlin_curvefit" and "leasqr" to > fit the data one row(or column) at a time. Now I would like to fit > the entire surface to an equation that is a function of both time > and wavelength. > > The inputs of the function leasqr are leasqr(*x,y,pin,f*). Y will > be the 256x433 signal data, pin will be my initial parameter > guesses and f will be my function handle. The problem I am having > is the x vector(s) for independent values. This is a function of > both the wavelength and time variables. > > What can I put in for the x argument so that the leasqr function > fits the entire matrix? > > Thank you Joel > > > > -- View this message in context: > http://octave.1599824.n4.nabble.com/Surface-fitting-tp4668758.html  > Sent from the Octave - General mailing list archive at Nabble.com. > > _______________________________________________ Help-octave mailing > list [hidden email] > https://lists.gnu.org/mailman/listinfo/help-octave> Hi Joel, the 'x' vector is not actually used for fitting and just handed through to your model function, so you are more or less free to put in what you want. Especially leasqr might check that the dimensions are equal to 'y' though, and complain if otherwise. nonlin_curvefit might be more flexible, but I cannot try it out right now. You can always wrap your model function before giving it to the fitting routines to use multiple independent variables: [...] = nonlin_curvefit( @(p,x) MyModel(p,lambda,t), pin, [], y); (Not sure if empty vector for 'x' works. If not, give 'y' again as an ugly trick ...) The other and probably cleaner possibility is to use nonlin_residmin, in that case you would need to calculate the residuals on your own: [...] = nonlin_residmin( @(p) (MyModel(p,lambda,t) - y).^2 ./ errors.^2, pin); Hope it helps, Markus _______________________________________________ Help-octave mailing list [hidden email] https://lists.gnu.org/mailman/listinfo/help-octave