gnuplot basics
Best, simplest, very powerful plotter (and more)
Can easily plot formulas or data_files or both! few plotters can do it so simply!

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gnuplot> plot "File"   will plot column 1 as x , col 2 as y of a file named "File"
  or can specify which columns of multicolumn file:
gnuplot> plot "File" u 3:1 w lines lt 1 lw 2
  will plot using column 3 as x and 1 as y   with lines, in red (lt 1), line_width 2

Can plot formulas directly:
gnuplot> R(x) = 1/(1+x**2)     formula to plot (Runge function)
gnuplot> plot R(x)     default xrange is [-10:10]
  Can specify desired xrange [-5:5] , in blue (lt 3), lw 4:
gnuplot> plot [-5:5] R(x) lt 3 lw 4

Can plot several graphs on same plot:
  formulas, and/or formulas and files: use comma in-between:   plot "file" , R(x) , ...   e.g.
gnuplot> G(x) = exp(-x**2)     another formula to plot (Gaussian, bell curve)
gnuplot> plot R(x) , G(x)   (on default xrange, default colors)
  Better: specify xrange, colors, line_widths:
gnuplot> plot [-5:5] R(x) lt 1 lw 3, G(x) lt 2 lw 4  

Set/unset xrange , yrange :   on plot line:
gnuplot> plot [-5:5] [-0.2:1.2] R(x) lt 1 lw 3 , G(x) lt 2 lw 4
  or each one separately:
gnuplot> set xrange [-6:6] ; plot R(x) lt 1 lw 3, G(x) lt 2 lw 4
gnuplot> set yrange [-0.1:1.1] ; plot R(x) lt 1 lw 3, G(x) lt 2 lw 4
gnuplot> unset yrange ; replot

Set xlabel, ylabel, title:
gnuplot> set xlabel 'x' ; set ylabel 'y'
gnuplot> set title 'Runge R(x) and Gaussian G(x)'
gnuplot> replot     (re-plot last plot)

See links on course page for more...