Hi Christian, Root is not currently instrumented to achieve what you want automatically. You have to give some initial values for the parameters. We had developped many years ago a very nice program called MUDIFI. This program was written in Fortran and it would be a nice addition to Root. I have no time to do this work now. However, if somebody is interested, I can provide some guidance. Rene Brun Christian Kaiser wrote: > > Hi, > I have to perform a regression to experimental data, which is presented in a > number of vectors of dimensionality five (x1,x2,x3,x4,x5,x6). This data should > be approximated by a function of the form > > x6=a * x1^b * x2^c * x3^d * x4^e * x5^f + g*x1^h.... and so on > > with parameters (a,b,c ...). The problem is, that fitting with an algorithm like > finding the steepest gradient from the starting-point to minimize chi squared, > is not possible, because I have no guess of appropriate starting points. I would > be grateful, if someone could tell me, if ROOT was able to deal with this kind > of problem und if it has advances compared with some standard software like SAS. > Thanks in advance > Christian Kaiser
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