Hi everybody, I am working on a fuel cell model. Right now I have implemented a regression member function in a "Fuelcell" class (I work in C++ with the static-function hack for GSL).
The Regressor( ) should, given some observations, find out the best parameters (there are 8, 7 of the cell plus the inductance of the wiring) of a impedance test, which is used to extract data useful for cell modelling. The underlying Fuelcell is quite nasty - there are two brent and one steffenson iteration loops below that level. All parameters, to have any meaning, must be > 0. The various _f, _df and _fdf of the LM loop return GSL_EDOM if any parameter is < 0, and also print out which parameter is bad and with what value. What happens is that the algorithm cycles between two values for the cathode-side diffusion-layer thickness, i.e. -246.626 and -0.65914 (metres). This might have to do with the fact that the diffusion layer is not very important for the data set I'm working in. How to I tell LM to stay away from the negative domain? Cheers, -Federico PS- I noticed there are no derivative-free nonlinear regression methods. I happen to have a paper from 1978 about DUD, exactly such an algorithm. Is does not even seem too difficult to implement. Is there interest to include such an algorithm?
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