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February 12th, 2009, 02:11 AM  #1 
Newbie Joined: Feb 2009 Posts: 1 Thanks: 0  fit one nonlinear function to four datasets
Dear all, I encountered a math problem when trying to find a set of robust and accurate parameters for a PDF, a nonlinear function with 3 parameters. The problem is: I have 4 datasets (X1,Y1), (X2,Y2),(X3,Y3),(X4,Y4) for a certain distribution. Each set, (Xi, Yi), contains about 400 data and was obtained from a different observational experiment. So it is assumed that different datasets should have different error variance. I am trying to use nonliner regression to obtain an empirical function from the four data sets. As the variance in each data set is unknown, it is impossible to obtain a weighting coefficient if i put them together. Is there any other solution for this case ? The empirical function is a*X^b/(1+exp(c*X)). I will appreciate very much if some could give me some support. Thank you! Sam 

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datasets, fit, function, nonlinear 
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