Nonlinear Fit Problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg7221] Nonlinear Fit Problem*From*: peter.geissler at iwr.uni-heidelberg.de*Date*: Fri, 16 May 1997 02:31:24 -0400 (EDT)*Organization*: InterNetNews at News.BelWue.DE (Stuttgart, Germany)*Sender*: owner-wri-mathgroup at wolfram.com

Hi everybody, I have to fit the function A / ((x-B)^C) (x = independent variable, A,B,C parameters) to a given dataset. I tried to use the NonlineaFit function from the Statistics'NonlinearFit' package, but did not not succeed. I tried data = {{x1,y1},{x2,y2},......} with {x,y} beeing my actual data NonlinearFit[data, A / ((x-B)^C), x, {A,B,C}] I have two major problems: 1) the fit does not converge to reasonable parameters. 2) I cannot specify any start values. I tried to give them as {{A,1000.0},{B,0.0},{C,1.0}} and similiar forms, but always got error messages concerning the parameters. 3) mathematica shows kind of a strange behavior when repeating the fit operation, sometimes it keeps old values, sometimes it reports different error messages or does not succeed on simpler fits which worked before. Any help welcome, Peter -------------------------------------------------------------------------------------- Peter Geissler IWR - Univ. of Heidelberg peter.geissler at iwr.uni-heidelberg.de -------------------------------------------------------------------------------------