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From: sfeam <sfeam@users.sourceforge.net>
Newsgroups: comp.graphics.apps.gnuplot
Subject: Re: gaussians as plotting style
Followup-To: comp.graphics.apps.gnuplot
Date: Fri, 10 Feb 2012 08:07:25 -0800
Organization: gnuplot development team
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Martin Keiter wrote:

> Hi,
> 
> background: I'm doing theoretical calculations of absorption spectra.
> The results are sharp lines (energy vs. absorption strength).
> Experimental data does in many cases not have sharp lines, but broader
> absorption. many small absortions in a small energy range may add up
> to a bigger absorption band.
> In order to better compare with experiment, I want to have broadened
> lines.
> 
> I have a file with x0/i value pairs in every line.
> for every pair of x0/i I want to plot i * )exp(-(x0-x)**2
> 
> And then I want to have a sum of all these plots (as in "smooth
> frequency")
> 
> I have tried
> 
> filename = "1a"
> lines = system(sprintf("wc --lines %s | sed 's/ .*//'", filename))
> plot for [line=1:lines] (\
> x0 = system(sprintf("awk '{if (NR==%d) print $%d;}' < %s " , line, 1,
> filename)),\
>  i = system(sprintf("awk '{if (NR==%d) print $%d;}' < %s " , line, 2,
>  filename)),\
> i* exp(-(x-x0)**2) )
> 
> but this is incredibly slow for a data file with 5 lines:
> 1 1.1
> 2 2.2
> 3 3.3
> 4 4.4
> 5 5.5
> 
> And it looks incredibly ugly!
> 
> can it be done in a more clever way? 

Why not just revise the input file to say
 f1(x) = 1 * exp(-(1.1-x)**2)
 f2(x) = 2 * exp(-(2.2-x)**2)
 f3(x) = 3 * exp(-(3.3-x)**2)
 ...
And then
gnuplot> load "defs.dat"
gnuplot> plot f1(x)+f2(x)+f3(x)...

If you like processing things with awk on input, this could 
even be constructed on the fly from your original data file.

gnuplot> load "< awk 'some-complicated-substitution-that-defines-f'"
gnuplot>  plot f1(x)+f2(x)+f3(x)...




> Best thing wohl be if gnuplot
> would accept a user defined function for the style, but I think that's
> not possible...?