gnuplot-info

[Gnuplot-info] How to find root or intersection of data plots

[<lyn...@fr...>]

Hello!


Is  there  a  possibility  to  determin  the  root  of  a  data  plot  or  the
intersections of two plots depending on the interpolation type that was chosen
for plotting? Is that possible with gnuplot or another free linux tool?
I know it is tricky to define the intersection points for data plots since the
intersection mostly depends on the interpolation type and is rarly exactly  on
a  data  point.  Still it is often necessary to estimate the intersection of a
data plot with another or with a function.
It would be already helpful to know the two data points in between  which  the
intersection  would  lie.  I  guess  for  the  problem  of  finding  the  root
(intersection of a plot with the x-axis) it would just be a problem of finding
the pairs of adjacent points where thy y-value chages sign.
Any  way to  do that with gnuplot or another tool? Still, having an evaluation
possibility depending on the gnuplot interpolation type (eg.  straigth  lines,
splines or kdensity) would be great.

Thanks for any help or hints about this.
Lynx

[Gnuplot-info] How to automatically compute root or intersection of data plots

[<lyn...@fr...>]

On 20/10/10 13:32:41, Marek W. Gutowski wrote:
> The simplest thing is to plot whatever is of interest and then
> to use mouse for zooming the area in question. Read current
> mouse pointer coordinates in the lower left part of plot.
> Zoom again, if still not satisfied.

Thanks  Marek  for  Your  answer. I seem to have asked it a bit unpresize. I'd
need  an         automatic/computational  evaluation  where  two  data   plots
intersect or where the difference of the two has its roots. Reading it off the
plot is OK for a few plots but if You need   to evalutate a big load  of  data
it would be nice to have a program doing that for You.

Can that be done with gnuplot or any other linux tool?

Thanks for any help or hints.
Lynx

> lyn...@fr... wrote:
>> Is  there  a  possibility  to  determin  the  root  of  a  data  plot  or  the
>> intersections of two plots depending on the interpolation type that was chosen
>> for plotting? Is that possible with gnuplot or another free linux tool?
>> I know it is tricky to define the intersection points for data plots since the
>> intersection mostly depends on the interpolation type and is rarly exactly  on
>> a  data  point.  Still it is often necessary to estimate the intersection of a
>> data plot with another or with a function.
>> It would be already helpful to know the two data points in between  which  the
>> intersection  would  lie.  I  guess  for  the  problem  of  finding  the  root
>> (intersection of a plot with the x-axis) it would just be a problem of finding
>> the pairs of adjacent points where thy y-value chages sign.
>> Any  way to  do that with gnuplot or another tool? Still, having an evaluation
>> possibility depending on the gnuplot interpolation type (eg.  straigth  lines,
>> splines or kdensity) would be great.
>>
>> Thanks for any help or hints about this.
>> Lynx
>
> -- 
> Marek W. Gutowski
> Institute of Physics PAS, ON-3.2, Al. Lotnikow 32/46
> 02-668 Warszawa, Poland, tel. +48-22-0228436601 ext. 3122
> == To talk or not to talk?  Yes, talk, plain ASCII please ==
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~