Re: [Gnuplot-info] Help request - linear regression giving screwy results

[Eric R. <es...@th...>]

Thomas Sefzick <t.s...@fz...>:
> 
> on the x-axis you have seconds since 2000-01-01, so your x-values
> are around 315360000.
> your y-values are around 20.
> 
> this leads to parameters which are different by at least 7 orders of
> magnitude.
> 
> to bring the parameters into the same range, subtract 10 years and scale the
> resulting x-values:
> 
> offset=10*365*24*60*60
> f(x)=1.e-7*m*(x-offset)+b
> m=7.
> b=6.
> fit f(x) 'comscore.dat' using 1:2 via m,b

Thank you, that does solve the problem.  I take it the failure of the
fit to converge properly was a result of some internal problem due
to floating-point limitations?

It seems as though this might be a general issue with plots using
time-valued x data. Might I suggest we do a FAQ entry on this topic?
If you were to post a draft here I would read and try to polish it it
for comprehensibility from a user point of view.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>