How to use gnuplot (gnu1)

How to use gnuplot

gnuplot is a public domain plotting program from the Free Software Foundation. It runs on most systems, except of Macintosh, which is boycotted by the FSF. It is a powerful program, among other things it produces very good postscript files, which can be used in the LaTeX files.
Special information:
Gnuplot Task 1........ Gnuplot Task 2
Gnuplot Task 3........ Gnuplot Task 4........ Functions in Gnuplot (and Fit) 
CALL:      gnuplot
           opens the command line interface
           usually anounces the standard terminal driver
           On the first   'plot' command opens the graphical window
           About postscript, see below
There is a number of examples in the working directory. Most important commands: 
To load a prepared file of commands:        load "probabs.com"

To plot a set of data from a file  :         plot "probabs"
                                             plot "probabs" using 1,4
                                             plot "probabs" using 1,4 with lines
When you change for example xrange (clear meaning, set xrange [0:6], you can redraw the picture by replot or rep. There is a very good help system. Type help to start learning. Now we copy a command set, illustrating use of USER-DEFINED constants and functi ons: 
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# This script demonstrates user defined variables
# and user defined functions
a=7      # user defined
d=3      # user defined
f(x)=a*exp(-d*x*x)  # user defined
set xrange [-2:2]
set yrange  [0:a]
plot f(x)
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You can paste this directly as an input under gnuplot. The sign '#' starts a c ommand You can redefine a constant any time later. This can be used for visual fitting. 
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# Example of visual fitting:

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a=0.325
plot "data",f(x)
a=0.350
replot
a=0.375
rep
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until you have found a good value of a. 
To copy the existing picture to a PostScript file:
(To produce an encapsulated postscript file)
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set terminal postscript eps monochrome "Courier"  18
set output "fiename.eps"  # otherwise writes the postscript into the screen
set size 1.8,1       # for plots which have a long x-axis
replot
set terminal x11     # closes fiename.eps and comes back to X11
replot
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