Re: [Gnuplot-info] Fit trouble when I use xdata time (fit isn't so good)

[GPS <gpo...@gm...>]

Hi Mr Thomas


Thank you very much for help me. Your tip helps a lot!

Have a very nice day!
__________________________________
Guilherme Poleszuk dos Santos Rosa


2010/2/23 Thomas Sefzick <t.s...@fz...>

>
> just set the 'origin' of the fit in the middle of your time data:
>
> toffset=strptime("%Y/%m/%d %H:%M","2010/02/20 23:28")
> f(x)=a + b*(x-toffset)
> fit f(x) "watthour.txt" using 1:4 via a,b
>
> so that 'a' and 'b' are not influencing each other.
>
>
> Guilherme Poleszuk wrote:
> >
> > Hi!
> >
> > I am a new user of gnuplot and my version is 4.2 patchlevel 6. I'm having
> > a
> > trouble with "fit" function when I use xdata time as X axis values. Here
> > my
> > script and data set.
> >
> > # watthour.gnu
> > # =========== < cut here
> > reset
> > set terminal png size 800,500 font comic 12 enhanced truecolor
> > set output "watthour.png"
> > set xdata time
> > set timefmt "%Y/%m/%d %H:%M"
> > set label "Powered by GnuPlot 4.2" at graph 0.87,-1.7 center font
> > "lhandw,10"
> > textcolor rgb "#800080"
> > show label
> > set key below left vertical title "Variables"
> > set border 3
> > set xtics rotate by 45 offset graph -0.075,-0.30 textcolor rgb "#008000"
> > nomirror
> > set ytics nomirror textcolor rgb "#008000" nomirror
> > set format x "%d%b %Hh"
> > set format x "%N"
> > set format y "%6.1f"
> > set xtics 86400
> > set ytics 2
> > set mxtics 12
> > set mytics 5
> > f(x)=a + b*x
> > fit f(x) "watthour.txt" using 1:4 via a,b
> > set title "Kilowatts - 2010\n Fit Model: f(t) = a + b.t " font "comic,
> 12"
> > textcolor rgb "#800080"
> > plot f(x) t"Projection" with lines 2, "watthour.txt" using 1:4 t "KWh"
> > with
> > points 3
> > # =========== < cut here
> >
> >
> >
> > # watthour.txt
> > # =========== < cut here
> > #YYYY MM DD hh mm U  KWh
> > 2010/02/19 23:36 3 22835.1
> > 2010/02/20 08:05 3 22839.0
> > 2010/02/20 10:32 3 22839.8
> > 2010/02/20 11:32 3 22840.1
> > 2010/02/20 12:49 3 22840.8
> > 2010/02/20 23:28 3 22845.5
> > 2010/02/21 01:40 3 22846.8
> > 2010/02/21 13:45 3 22851.5
> > 2010/02/21 22:09 3 22855.6
> > 2010/02/22 18:06 3 22864.5
> > 2010/02/22 22:14 3 22866.0
> > # =========== < cut here
> >
> >
> >
> > I believe that are a problem with "fit" function when I use xdata time,
> > because X values are converted to second since 2000/01/01 ( I think! )
> and
> > this number get big compared to Y values... the algorith to "fit" the
> data
> > to
> > the model has some dificulties with this. The curve not pass near of the
> > points, of course, it not pass over them, but should be pass so near
> > because
> > it is a adjustment with "least squares"!! My data set file don't have
> > outliers
> > to cause the problem that I report here.
> >
> > I tried do some tests with this same data, changing time near year 2000
> > and
> > the fit curv was diferent, but it curve should be the same angular
> > coeficient.
> > Is it a bug or I'm commiting a mistake.
> >
> > Thank you very much!
> >
> > __________________________________
> > Guilherme Poleszuk dos Santos Rosa
> > São Paulo, Brazil
> >
> >
> >
> ------------------------------------------------------------------------------
> > Download Intel&#174; Parallel Studio Eval
> > Try the new software tools for yourself. Speed compiling, find bugs
> > proactively, and fine-tune applications for parallel performance.
> > See why Intel Parallel Studio got high marks during beta.
> > http://p.sf.net/sfu/intel-sw-dev
> > _______________________________________________
> > gnuplot-info mailing list
> > gnu...@li...
> > https://lists.sourceforge.net/lists/listinfo/gnuplot-info
> >
> >
>
> --
> View this message in context:
> http://old.nabble.com/Fit-trouble-when-I-use-xdata-time-%28fit-isn%27t-so-good%29-tp27698343p27702229.html
> Sent from the Gnuplot - User mailing list archive at Nabble.com.
>
>
>
> ------------------------------------------------------------------------------
> Download Intel&#174; Parallel Studio Eval
> Try the new software tools for yourself. Speed compiling, find bugs
> proactively, and fine-tune applications for parallel performance.
> See why Intel Parallel Studio got high marks during beta.
> http://p.sf.net/sfu/intel-sw-dev
> _______________________________________________
> gnuplot-info mailing list
> gnu...@li...
> https://lists.sourceforge.net/lists/listinfo/gnuplot-info
>