I think my point was more that if I specify "y,5" for the y, which is close 
to 50% of the values, then I get a reasonable result while if the default 
5% is used, then I don't.  Or did I miss something?



On Wednesday 26 November 2014 13:39:16 Jeremy Sanders wrote:
> On 26/11/14 13:31, Fred Labrosse wrote:
> > Thanks, that did it.  Interestingly enough, the console said "Warning:
> > No errors on y values. Assuming 5% errors", which I thought was
> > appropriate. Clearly not.
> > 
> > However, it seems that whatever value I specify as an error makes it
> > work. y,5 gives more or less the same as y,0.1...
> Yes, it's 5% not 10%. The reason it fails with fractional errors is that
> the lower the y value the lower the uncertainty. Your outliers have low
> y values and so they get extra weight because they have lower
> uncertainties. Any sensible constant y uncertainty value should work for
> your data.
> A default constant error would have been better. Most of my data is
> fitting powerlaws, where the uncertainties are typically fractional, so
> that's probably why I chose that default.
> Cheers
> Jeremy

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