Gnuplot

From UC_Chemistry

1 Data Fitting
2 Surface Plots
3 XY plot options
4 Terminals
5 Notations
6 External links

Data Fitting

Fitting your data with a function. Suppose you have file force.dat containing two columns of data (x and y). Let's fit the data with linear function f1 and initial guess of parameters.

$ gnuplot
gnuplot> f1(x) = a1*x +b1
gnuplot> a1 = 300; b1 = 0.005;
gnuplot> fit f1(x) 'force.dat' using 1:2 via a1, b1

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Surface Plots

If you have a function of two variables f(x,y) save the data in file mydata in the following format

x0 y0 f
x0 y1 f
...
x0 yn f
        
x1 y0 f
x1 y1 f
...
x1 yn f
      
...

Having mydata you can plot surfaces as

gnuplot> set style data lines
gnuplot> splot 'mydata'

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XY plot options

set title 'mytitle'
set xrange [0.001:0.005]
set yrange [1:2] 
set xlabel "my xlabel"
set ylabel "my ylabel"
set label 1 "high" at 0.002,1.5

subscript, superscript and greek letters

set xlabel "t_{1/2}"
set ylabel "x^2"
set title "{/Symbol a}decay"

multi-plot

p "decay1.dat" u 1:2 t "alpha decay", "decay2.dat" u 1:2 t "beta decay", "decay3.dat" u 1:2 t "gamma decay"

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Terminals

You've probably noticed that gnuplot always outputs (by default) to an X11-window. This can be changed with the set term command, instructing gnuplot to write its output to a file instead.

set term png medium size 800,600
set out "bob.png"
replot

will output a fairly ugly-looking png file of your plot. I think this is because most of the development has gone into the ps terminal, where some nice fonts are (or should be) avaialble.

set term postscript enhanced color solid lw 2 "Times-Roman" 27
set out "bob.ps"
replot

This is the current "best-practices" terminal I have found so far. You will probably have to run the GIMP to make it the right size and/or make the background transparent.

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