Hi Michel, You can do this by using Minuit directly as illustrated in the test program at $ROOTSYS/test/minexam.cxx. Define a function FCN computing the sum of the two chisquares with the funcions f_A and f_B defined as you indicate. If you need more help, please send me a short script creating your two sets of points and also with the definitions of f_A and f_B + the initial values for the parameters. Rene Brun On Wed, 25 Sep 2002, [iso-8859-1] Michel Perrin wrote: > > > Hi Rooters, > > I need to simultaneously fit two independent data > sets : > > A:(xa_i,ya_i), i=0...N_A > > B:(xb_j,yb_j), j=0...N_B > > with two similar functions : > > f_A(p_A, par0, par1,...,parn) to describe data set A > > f_B(p_B, par0, par1,...,parn) to describe data set B > > The two functions have the same expression, and share > the same parameters : they differ by only one > parameter (the first one). Of course I can fit > independently A with f_A and B with f_B. But what I > need is the common parameters values (par0,... parn) > and values of (par_A, par_B) that fit simultaneously > the two datasets, i.e. that minimize the combined > chisquare (sum of the 2 chisquares). > > I have tried different methods (and sometimes > awful tricks) with Root but failed to write > a working program. > > Is there an easy way to do this with Root ? > > Michel > > > > ___________________________________________________________ > Do You Yahoo!? -- Une adresse @yahoo.fr gratuite et en français ! > Yahoo! Mail : http://fr.mail.yahoo.com >
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