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Re: adding constraints to curve fitting / least squares code?
Posted:
Mar 9, 2013 4:53 PM


"Andres " <adelahoz@gmail.com> wrote in message <khf2ka$mtq$1@newscl01ah.mathworks.com>... > Hello. > > I am using the curve fitting tool's generated code to obtain coefficient values for different functions that I'm adjusting to some data. > > One problem I often encounter with the data sets, though, is that the best fit that the code finds for the coefficients leads to a negative slope at the very beginning of the data. Since I'm doing this to obtain a material model, this initial negative slope doesn't really make sense and will cause computing problems when I use the coefficient values in a model. So the ideal solution would be to make the code such that the slope is always positive in the range of the minimum and maximum xvalues. > > I can solve this by constraining the coefficient values either on CFTOOL or in the code itself. But I'd prefer to do it automatically, by a code, since this way I have to keep rewriting things. Is there an 'easy' way of doing this (i.e. adding a code to the current cftoolgenerated code that forces a condition), or would I have to start from scratch? > > This is a sample of the code: >
(snip)
> > Any help would be appreciated.
Use a tool (SLM) that is designed from the start to help you do this.
http://www.mathworks.com/matlabcentral/fileexchange/24443slmshapelanguagemodeling
If you want the slope to be nonnegative at the left end, there is a simple way to specify that.
HTH, John



