Re: processing data for gnuplot

[Paul E Condon <pecondon@peakpeak.com>]

On Wed, Dec 17, 2003 at 01:57:22PM +0100, David Fokkema wrote:
> Hi group,
> 
> I was not entirely sure what to put in the subject line...
> 
> I did a very simple physics experiment involving two strings, two
> weights and one pulley. I'll spare you the details, but by varying one
> of the two masses, I measured the angle one of the strings made with the
> vertical. I got these results:
> 
> # m2      alpha
> 0       0
> 10      12
> 20      23
> 30      32
> 15      18
> 25      27
> 12      14
> 22      24
> 27      29
> 17      20
> 
> where the first column is the mass of the second weight and alpha is the
> angle, in which I made an error of ±1 degree. So far, so good.
> 
> Now, I want to plot in gnuplot the following: m2 along the x-axis, but
> the tangent of alpha with errorbars along the y-axis. So, I have to
> process this data somewhat further to obtain a second data file with
> three columns: m2, tan alpha-low, tan alpha-high.
> 
> Of course, I could use gnumeric or something like that, but I'm
> wondering if there are command-line tools out there that could do the
> job. Or should I use a scripting language? perl? awk? bc? Efficiency is
> not the problem here, ease of use is.
> 

The command-line tool to use is awk. e.g.

awk ' {print $1, $2-D, $2+D;} ' infile >outfile

where D is the deviation in alpha. D can be computed by a subroutine
function, but I don't have enough info to write plausible example code.

HTH


-- 
Paul E Condon           
pecondon@peakpeak.com