Question: Nonlinear fit not working right

Hello everyone

I have a function, constructed by numerically solving a set of differential equations.  I need to find a best fit for this function with an analitic model with two parameters. I tried to extract some points of this function and then using nonlinearfit:

xvalues:=Vector([seq(105 ..106,104);

yvalues:=Vector([seq(evalf(function),x=105 ..106,104)]);

with(Statistics):

NonlinearFit(model,xvalues,yvalues,x,output=[parametervalues,residuals]);

but it tells me that it encountered complex values. I know that there's a fit, but how do I circunvent this problem

thanks for the help

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